CO 


CM 
O 


LIBRARY 


UNIVERSITY  OF  CALIFORNIA. 

Jtt 

Class 


I. 

A  STUDY  OF  SOME 
NEW  SEM1PERMEABLE  MEMBRANES 

II. 

EXPERIMENTS  ON  THE  PREPARATION  OF 

POROUS  CUPS  SUITABLE  FOR  THE 
MEASUREMENT  OF  OSMOTIC  PRESSURE 


DISSERTATION 

SUBMITTED  TO  THE  BOARD  OP  UNIVERSITY  STUDIES  OF  THE  JOHNS 
HOPKINS  UNIVERSITY  IN  CONFORMITY  WITH  THE  REQUIRE- 
MENTS FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY 


ELLIOT  SNELL  HALL 

il 


or  THE 
(  UNIVERSITY  ) 


BALTIMORE,  MD. 
1904 


PRESS  OF 

THE  NEW  ERA  PRINTING  COMPANY 
LANCASTER.  PA. 


ACKNOWLEDGMENT. 

To  Professor  Morse,  for  his  kindly  instruction  both  in  labo- 
ratory and  lecture  room,  the  writer  desires  to  express  his  sincere 
gratitude. 

He  would  also  acknowledge  his  great  indebtedness  to  Presi- 
dent Remsen,  Professor  Renouf,  Professor  Jones,  Professor 
Shattuck  and  Doctor  Frazer. 


iii 


CONTENTS. 


INTRODUCTION     . .5 

I.  A  STUDY  OF  SOME  NEW  SEMIPERMEABLE  MEMBRANES. 

Cells 8 

Solutions  Used  in  the  Formation  of  Membranes     .         .  .9 

Electrodes     .......  .     9 

Removal  of  Air  from  the  Cell  Wall        ...  .9 

The  Deposition  of  the  Membrane  .         .         .         .         .  .10 

Methods  of  Measuring  the  Activity  of  the  Membranes  .  .11 

Membranes    .         .                  ,         .         •         .         .         .  .12 

Uranyl  Phosphate          .         ....         .         .         .  .12 

Potassium  Diuranate     .         .-        .       -  .,"     ;         .   '.-"— —  .   15 

Stannous  Hydroxide      .         ,         .         .         .         .         .  .16 

Silver  Cobalticyanide     .         .         .         .         •.'..,.         .  .18 

Manganese  Cobalticyanide    .         .         .         .         .         .  .  19 

Zinc  Cobalticyanide       .         .         .         .         .         .         .  .  .   19 

Cadmium  Cobalticyanide       .         .         .         .         ..       .  .  21 

Mercurous  Ferrocyanide        .         .                  .         .         .  .  22 

Silver  Ferrocyanide       .                   .         .         .         ...  .22 

Stannous  Ferrocyanide .         .         .         .         .         .         .  .  23 

Uranyl  Ferrocyanide     .         .         ....         .  .25 

Conclusions  .         .         .         .                  .         ,         .         .  .31 

II.  EXPERIMENTS    ON    THE    PREPARATION   OF    POROUS  CUPS 

SUITABLE  FOR  THE  MEASUREMENT  OF  OSMOTIC  PRESSURE. 

The  Mould    .         .         .         .         .         .         .         .         .  .34 

Dimensions  of  the  Cup           .         .         .         .         .         .  .35 

The  Electric  Furnace    .         .         .         .         .         .         ,  .35 

Calibration  of  the  Electric  Furnace        .         .         .         .  .  38 

The  Gas  Furnace           .         .         .                . .         .         .  .41 

Observations  on  the  Burning  of  Cells    .         .         .         .  .42 

BIOGRAPHY  .  .54 


IV 


Of  THi 

1   VN/VEK8ITY 


INTRODUCTION. 

The  study  of  osmotic  pressure  which  was  begun  in  this 
laboratory  by  Morse  and  Horn  in  1901,  has  been  continued  by 
Morse  and  Frazer  and  others  in  the  face  of  difficulties  much 
more  numerous  and  more  serious  than  were  anticipated  at  the 
outset. 

With  the  discovery  of  a  new  and  simple  method  for  the 
preparation  of  an  efficient  semipermeable  membrane  came  the 
necessity  for  a  suitable  support  for  the  septum  and  a  device 
for  the  accurate  measurement  of  the  high  pressures  developed 
within  the  cell. 

In  1901,  Morse  and  Horn1  showed  that  a  strong  membrane 
could  be  deposited  upon  or  within  the  walls  of  a  porous  clay 
cup  much  more  easily  and  with  greater  certainty  by  electrol- 
ysis than  by  the  diffusion  method  of  Pfeffer.  They  measured 
pressures  of  not  more  than  4.5  atmospheres,  but  there  was  no 
indication  that  the  limiting  strength  of  the  membrane  had  been 
reached  at  this  point.  It  was  apparent,  however,  that  the 
measurement  of  still  greater  pressures  was  dependent  upon 
some  more  effectual  means  of  attaching  the  manometers  to  the 
cups. 

In  view  of  the  very  high  pressures  which  were  subsequently 
obtained,  a  satisfactory  solution  of  this  problem  proved  to  be 
very  difficult,  but  it  was  accomplished  in  the  following  year  by 
Morse  and  Frazer,2  who,  after  repeated  failures,  devised  an  ap- 
paratus which  has  withstood  a  pressure  of  more  than  thirty- 
one  atmospheres  and  which  promises  to  be  equal  to  any  strain 
which  the  cells  themselves  will  bear. 

The  same  authors  also  undertook  a  more  careful  investigation 
of  the  cups  in  the  walls  of  which  the  membranes  were  de- 

lAmer.  Chem.  Jour.,  26,  80. 
2Amer.  Chem.  Jour.,  28,  1. 

5 


6  INTRODUCTION. 

posited  and  made  numerous  observations  on  the  measurement 
of  osmotic  pressures  of  half  normal  and  normal  solutions  of 
cane  sugar.  They  expressly  state,  however,  that  these  obser- 
vations "  have  thus  far  been  made  with  reference  to  the  testing 
of  the  construction  of  our  cells  and  the  efficiency  of  the  mem- 
branes prepared  by  the  electrolytic  process  and  not  with  a  view 
to  the  accurate  determination  of  the  pressures  of  such  solutions." 

Before  these  accurate  determinations  could  be  made  it  was 
necessary  to  perfect  the  porous  cup  which  served  as  a  support 
for  the  membrane. 

In  the  meantime,  another  important  phase  of  the  subject  was 
investigated.  Morse  and  Horn,  and  Morse  and  Frazer  had 
used  only  the  copper  ferrocyanide  membrane.  There  was  no 
reason  to  suppose  that  a  large  number  of  different  membranes 
might  not  be  found,  the  varying  chemical  properties  of  which 
might  make  possible  the  study  of  osmotic  pressures  of  a  much 
greater  variety  of  substances  than  would  otherwise  be  practic- 
able. 

Part  I.  of  this  dissertation  deals  with  an  investigation  of  these 
membranes. 

It  has  already  been  mentioned  that  one  of  the  most  difficult 
problems  to  be  solved  was  a  method  for  securing  the  manometer 
in  the  cell.  Another  problem,  one  which  has  been  beset  with 
obstacles  on  every  hand,  is  the  preparation  of  a  porous  cup 
which  can  be  relied  upon  to  satisfy  the  following  requirements  : 

1.  The  cup  must  be  very  strong.     Morse  and  Frazer,  work- 
ing with  a  normal  solution  of  sugar,   measured   pressures  of 
about  471   pounds  to  the  square  inch,  and  there  is  reason  to 
believe  that  even  greater  pressures  would  have  been  developed 
had  not  the  apparatus  been  shattered  at  this  point. 

2.  The  cup  must  be  made  of  very  finely  divided  materials. 
Microscopic  examination  of  cross-sections  of  cells  has  shown 
that  those  having  the  finest  pores  are  those  which  have  given 
the  most  satisfactory  results. 

3.  The  walls  of  the  cup  must  be  free  from  "  air-blisters  " 


INTRODUCTION.  7 

and  cavities.  It  is  obvious  that  at  the  point  where  a  membrane 
bridges  one  of  these  cavities,  it  finds  no  support  and  even  if  it 
offers  considerable  resistance  to  the  electric  current  used  in  the 
process  of  its  formation,  it  cannot  be  expected  to  withstand 
such  enormous  pressures  as  those  already  mentioned. 

After  unavailing  efforts  to  obtain  from  potteries  in  Boston 
and  Baltimore,  cups  which  would  satisfy  these  requirements, 
the  work  of  making  them  in  this  laboratory  was  undertaken, 
and  has  been  carried  on  since  the  spring  of  1903. 

Part  II.  of  this  dissertation  gives  an  account  of  numerous 
attempts  made  since  October  1,  1903,  to  prepare  cups  which 
would  be  free  from  the  defects  of  those  previously  used. 


I.     A   STUDY   OF    SOME    NEW   SEMIPERMEABLE 
MEMBRANES. 

CELLS. 

In  the  investigation  1  of  the  new  membranes,  two  kinds  of 
porous  cups  were  used  :  first,  bottle-shaped  cups  of  from  175 
to  200  cc.  capacity,  and  secondly,  small  hard-burned  cups 
such  as  had  been  employed  by  Morse  and  Frazer.  These  had 
an  effective  capacity  of  about  20  cc. 

The  walls  of  the  bottle-shaped  cells  afforded  such  a  poor 
support  for  the  membranes  deposited  upon  them  that  even  if 
the  cells  themselves  had  not  been  deficient  in  strength,  no  very 
high  pressures  could  have  been  developed  within  these  cups, 
without  rupture  to  the  membrane. 

They  did,  however,  afford  a  large  surface  for  the  deposition 
of  the  membrane,  and  hence  made  it  possible  to  test  the  activity 
of  the  latter  by  measuring  the  rate  at  which  a  sugar  solution 
was  delivered  from  the  cup  when  the  latter  was  immersed  in 
pure  water. 

These  larger  vessels  were  not  at  all  uniform  in  quality,  and 
when  broken,  revealed  in  almost  every  case  the  presence  of 
pores  and  air-blisters,  sometimes  as  large  as  the  head  of  a  pin. 
There  is  also  good  reason  for  believing  that  the  effective  area 
varied  from  cell  to  cell,  that  is,  that  certain  portions  of  the  wall 
were  not  porous,  and  hence  diminished  the  rate  of  endosmose  of 
the  solvent  to  a  corresponding  degree. 

On  account  of  this  lack  of  uniformity  in  the  texture  and 
porosity  of  the  cell  wall,  it  was  never  safe  to  condemn  a  mem- 
brane as  worthless  until  it  had  been  tried  repeatedly  in  differ- 
ent cells,  and  even  then  its  failure  to  show  activity  or  its  infer- 
iority to  other  membranes  of  different  composition,  might  be 

*R  F.  Carver,  Dissertation,  Johns  Hopkins  University  (1903);  J.  P. 
Coony,  Dissertation,  Johns  Hopkins  University  (1903). 

8 


REMOVAL    OF    AIR    FROM    THE    CELL    WALLS. 

attributed  to  imperfections  in  the  cell  quite  as  justly  as  to  the 
faulty  nature  of  the  septum. 

While,  therefore,  no  final  conclusions  as  to  the  relative  ex- 
cellence of  the  membranes  can  be  drawn  from  the  experiments 
which  are  described  in  the  following  pages,  this  investigation 
may  afford  a  basis  for  future  quantitative  work  which  will  be 
made  possible  by  the  acquisition  of  satisfactory  cells. 

SOLUTIONS  USED  IN  THE  FORMATION  OF  MEMBRANES. 

Unless  otherwise  stated,  the  solutions  used  in  the  preparation 
of  the  various  membranes  were  one-tenth  normal,  when  first 
made  up.  Of  course,  where  the  electrodes  were  of  platinum, 
the  strength  of  the  solutions  in  which  they  were  immersed  be- 
came constantly  less.  The  solution  around  the  cathode  was 
frequently  renewed  in  order  to  prevent  the  accumulation  of 
alkali. 

The  potassium  ferrocyanide  employed  was  recrystallized 
several  times  from  the  commercial  product,  The  cobalticyan- 
ide  was  prepared  from  cobalt  nitrate  and  potassium  cyanide  and 
was  also  purified  by  recrystallization.  The  other  salts  used  in 
the  preparation  of  the  various  solutions  were  taken  from  the 
regular  laboratory  supply. 

ELECTRODES. 

Wherever  practicable,  the  anode  was  of  the  same  metal  as 
that  of  the  salt  in  which  it  was  immersed,  but  in  most  cases 
both  anode  and  cathode  were  of  platinum.  The  outer  electrode, 
which  was  large  enough  to  surround  the  cup  without  touching 
it,  was  usually  made  the  anode ;  the  other  was  about  5  cm.  in 
length  and  was  placed  within  the  cell. 

REMOVAL  OF  AIR  FROM  THE  CELL  WALL. 

The  air  was  removed  from  the  cell  wall  by  the  method  of 
Morse  and  Horn,  which  is  briefly  as  follows. 

The  cell  was  filled  with  a  dilute  solution  of  potassium  sul- 
phate and,  surrounded  by  the  platinum  anode,  was  placed  in  a 


10  A   STUDY   OF   SEMIPEBMEABLE    MEMBRANES. 

beaker  containing  a  sufficient  quantity  of  the  same  solution  to 
cover  the  cell.  The  cathode  was  inserted  and  a  110- volt  cur- 
rent passed  until  from  200  to  500  cc.  of  the  solution  had  been 
forced  by  endosmose  through  the  porous  walls,  in  the  direction 
of  the  current.  The  form  of  apparatus  which  was  used  is  given 
in  detail  below  where  the  method  of  depositing  the  membrane 
is  described. 

The  cell  was  next  removed  from  the  solution  and  emptied, 
and  after  washing  within  and  without  with  distilled  water  was 
set  up  as  before,  except  that  pure  water  was  used  now  in  place 
of  the  sulphate  solution.  The  current  was  then  passed  until 
the  high  resistance  indicated  the  almost  complete  removal  of 
the  salt  from  the  walls  of  the  cell.  If  the  membrane  was  not 
immediately  deposited,  the  cell  was  kept  in  distilled  water  until 
required  for  use. 

THE  DEPOSITION  OF  THE  MEMBRANE. 

The  inside  surface  of  the  neck  of  the  cell  was  first  coated 
with  shellac  to  prevent  the  formation  of  a  membrane  where  it 
would  be  in  danger  of  rupture  when  the  stopper  was  removed. 
The  cell  was  then  fitted  with  a  rubber  stopper  through  which 
passed  one  end  of  the  cross-arm  of  a  T  tube.  The  stem  of  the 
tube  served  as  a  horizontal  outlet  for  the  liquid  which  flows  into 
the  cell  as  a  result  of  endosmose  when  the  electrical  connections 
are  established. 

Through  the  vertical  portion  of  the  T  tube  passed  both  the 
platinum  wire  which  was  welded  to  the  inner  electrode,  and  a 
piece  of  glass  tubing  which  reached  to  the  bottom  of  the  cell 
and  was  attached  to  a  funnel  of  convenient  size  at  the  upper  end. 

Through  this  tube  the  inner  electrolyte  was  introduced  from 
time  to  time,  while  the  membrane  was  being  deposited.  This 
precaution  was  necessary  in  the  case  of  membranes  which  were 
decomposed  by  the  alkali  which  accumulated  around  the 
cathode. 

The  cell  was  then  filled  with  the  potassium  sulphate  solution 


MEASURING    ACTIVITY    OF    MEMBRANES.  11 

already  mentioned  and  placed  within  the  larger  cylindrical 
electrode  in  a  beaker  also  filled  with  the  sulphate  solution. 
Connection  was  established  with  the  storage  battery  or 
dynamo  in  such  a  way  that  the  current  passed  from  the  outer 
to  the  inner  solution. 

After  the  air  and  the  potassium  sulphate  had  been  removed 
from  the  cell  wall,  the  latter  was  ready  for  the  deposition  of 
the  membrane. 

The  electrodes  were  connected  with  the  battery  terminals  and 
the  two  solutions  of  the  membrane-forming  salts  were  poured, 
as  nearly  simultaneously  as  possible,  the  one  into  the  beaker 
and  the  other  into  the  cell. 

An  initial  electromotive  force  of  about  12  volts  was  usually 
employed.  This  was  increased  gradually,  in  some  cases  to  110 
volts,  in  others  to  a  smaller  number,  depending  upon  the 
strength  of  the  membrane. 

At  first  the  resistance  was  large,  owing  to  the  presence  of 
water  in  the  cell  wall,  but  as  the  electrolytes  began  to  fill  the 
pores,  the  current  increased  until  the  membrane  began  to  form. 
At  this  point  the  resistance  began  to  increase,  attaining  a 
maximum  in  anywhere  from  about  one  to  five  hours.  When 
this  was  reached  the  circuit  was  broken  and  the  cell  was  re- 
moved, washed  and  immersed  in  distilled  water  where  it  was 
kept  until  the  activity  of  the  membrane  was  tested. 

METHODS  OF  MEASURING  THE  ACTIVITY  OF  THE 
MEMBRANES. 

The  activity  of  the  membranes  was  tested  in  two  ways. 
The  first  of  these  was  used  only  with  the  small  cups  ;  the 
second,  exclusively  with  the  bottle-shaped  cells. 

1.  The  cell  was  closed  with  a  perforated  rubber  stopper 
through  which  passed  a  glass  tube  4  or  5  mm.  in  diameter 
and  about  75  mm.  in  length.  Into  the  end  of  this  tube  a  sec- 
ond perforated  rubber  stopper  was  fitted  and  through  the  latter 
a  length  of  capillary  glass  tubing  was  passed  until  its  lower 


12  A   STUDY   OF   SEMIPERMEABLE    MEMBRANES. 

end  was  flush  with  the  bottom  of  the  stopper.  The  cell,  hav- 
ing been  previously  filled  with  a  sugar  solution,  was  immersed 
in  water  and  the  height  to  which  the  solution  rose  in  the  capil- 
lary tube  was  measured. 

2.  The  cell  was  filled  with  a  sugar  solution  and  closed  with 
a  perforated  rubber  stopper  through  which  passed  one  end  of  a 
small  glass  tube  bent  to  two  right  angles.  The  outer  or  free 
end  of  the  tube  was  cut  off  at  such  a  point  that  it  was  always 
above  the  level  of  the  liquid  in  which  the  cup  was  immersed, 
thus  preventing  the  formation  of  a  siphon.  As  water  passed 
in  through  the  walls  of  the  cell,  a  corresponding  volume  of  the 
sugar  solution  was  forced  out  through  the  delivery  tube  and 
was  received  in  a  100  cc.  measuring  cylinder. 

In  the  later  experiments  gas  measuring  tubes  graduated  to 
fifths  of  a  cubic  centimeter  were  substituted  for  the  cylinders. 

MEMBRANES.1 

The  following  membranes  were  investigated  with  regard  to 
their  activity :  Uranyl  phosphate,  potassium  diuranate,  stannous 
hydroxide,  the  cobalticyanides  of  silver,  manganese,  zinc,  and 
cadmium  ;  the  ferrocyanides  of  mercury,  silver,  tin,  and  uranyl. 
An  attempt  was  made  to  prepare  membranes  of  stannous  and 
nickel  ferricyanide,  but  in  both  cases  the  ferricyanide  was  found 
to  be  reduced  and  the  cells  were  never  tested  for  osmotic  pres- 
sure. 

URANYL  PHOSPHATE. 

This  substance  is  precipitated  by  disodium  phosphate  from  a 
solution  of  uranyl  acetate,  as  a  pale  yellow,  gelatinous  mass 
which  is  easily  soluble  in  dilute  hydrochloric  acid,  but  insoluble 
in  dilute  acetic  acid. 

1  Morse  and  Coony  have  prepared  the  following  semipermeable  membranes 
by  the  electrolytic  method  :  ferric  hydroxide,  ferric  phosphate,  the  ferrocy- 
anides of  manganese  and  cobalt,  and  Prussian  blue. 

Morse  and  Carver  have,  by  the  same  method,  prepared  membranes  of  the 
phosphates  of  calcium  and  copper,  the  ferrocyanides  of  cadmium  and  nickel, 
the  sulphide  of  cadmium  and  the  cobalticyanides  of  cobalt,  nickel,  copper, 
and  iron.  For  details  concerning  these  membranes  vide  the  dissertations  of 
J.  P.  Coony  (1903),  and  B.  F.  Carver  (1903). 


URANYL    PHOSPHATE.  13 

The  uranyl  phosphate  membrane  was  deposited  in  one  of  the 
small  cups  which  for  the  purpose  was  immersed  in  a  solution 
of  uranyl  acetate  and  filled  with  a  disodium  phosphate  solution. 
The  current  was  passed  from  the  outer  to  the  inner  electrode. 

The  initial  electromotive  force  was  twelve  volts.  This  was 
increased  gradually  until,  in  fifty  minutes,  with  a  voltage  of 
110,  the  resistance  had  reached  2,000  ohms.  In  three  hours 
and  twenty  minutes  it  had  risen  to  6,500  ohms. 

The  cell  was  filled  with  an  approximately  half  normal  sugar 
solution,  and  set  up  with  an  open  manometer,  in  the  manner 
already  described.  No  pressure  was  obtained. 

The  cell  was  removed  from  the  uranyl  acetate  solution  and 
emptied,  and  after  being  rinsed  both  within  and  without  with  dis- 
tilled water,  was  subjected  again  to  the  membrane-forming  proc- 
ess in  exactly  the  same  manner  as  that  already  described.  For 
the  sake  of  convenience  this  process  will  hereafter  be  referred 
to  as  the  if  reenforcement "  of  the  membrane. 

With  an  electromotive  force  of  110  volts,  the  resistance  rose 
during  the  first  forty-five  minutes  to  10,000  ohms,  but  when 
tested  a  second  time  the  membrane  gave  no  evidence  of  activity. 
The  cup  was  broken  and  found  to  contain  a  yellow  membrane 
of  the  phosphate  just  beneath  the  interior  surface  of  the  cell 
wall. 

Another  membrane  of  identical  composition  was  deposited 
in  a  fresh  cell  of  the  same  type.  The  initial  voltage  of  the 
current,  10.5,  was  raised  during  the  course  of  the  first  hour 
and  a  half  to  111.  At  the  end  of  this  period  the  resistance 
amounted  to  2,900  ohms  and  afterwards  rose  to  a  maximum 
of  4,900  ohms. 

The  cell  was  set  up  as  before  and  this  time  the  membrane 
proved  to  be  active. 

The  observations  which  were  made  during  the  first  five  days  of 
its  activity  are  recorded  in  Table  I.  The  last  column  gives  the 
height  of  the  meniscus  in  the  capillary  tube,  above  the  water 
in  which  the  cell  was  immersed. 


14  A    STUDY    OF    SEMIPERMEABLE    MEMBRANES. 

TABLE  I. 


Dec.  15, 

5  :  10  p.  m. 

50  mm. 

It            U 

10:10. 

238 

"     16, 

3:30 

393 

"     17, 

4:35 

623 

"     20, 

3  :30 

889 

As  the  cell  was  set  up  in  a  room  which  was  not  heated  at 
night,  it  must  have  been  subjected  to  changes  of  temperature 
amounting  to  12°  or  15°  during  each  period  of  twenty-four 
hours. 

Although  allowed  to  stand  undisturbed  for  two  weeks,  the 
cell  never  developed  a  pressure  greater  than  that  recorded  on 
December  20. 

When  the  cup  was  broken,  the  membrane  was  found  to  be 
situated  about  one  millimeter  from  the  interior  and  two  milli- 
meters from  the  exterior,  surface  of  the  cell  wall,  and  as  far  as 
could  be  judged  from  its  appearance,  was  as  perfect  as  very 
much  more  active  membranes  of  diiferent  composition  prepared 
at  a  subsequent  date. 

As  far  as  tested  in  this  laboratory,  membranes  consisting  of 
calcium,1  copper 2  and  ferric  phosphate 3  have  proved  to  be  very 
much  less  active  than  would  be  expected  from  a  consideration 
of  the  gelatinous  character  of  these  substances  when  precipitated 
from  solutions. 

There  are  theoretical  reasons 4  for  believing  that  if  the  mem- 
brane had  been  deposited  directly  upon  the  inner  surface  of  the 
cell  instead  of  within  the  cell  wall,  the  rate  of  endosmose  of  the 
water,  and  possibly  the  final  pressure,  would  have  been  in- 
creased. 

Since  the  experiment  described  above  was  made,  the  question 
of  position  of  membrane  has  been  investigated  in  this  labora- 
tory by  Dr.  Coony,  who  has  shown  that  the  relative  concentra- 

1  B.  F.  Carver,  Dissertation,  Johns  Hopkins  University  (1903),  p.  13. 

2  Ibid.,  p.  14. 

3  J.  P.  Coony,  Dissertation,  Johns  Hopkins  University  (1903),  p.  16. 

4  Ibid. ,  p.  10. 


POTASSIUM    DIURANATE.  15 

tions  of  the  electrolytes  used  in  the  formation  of  the  membrane 
are  the  determining  factors  in  the  case.  "  By  using  high  rela- 
tive concentrations  within  [the  cell]  the  precipitate  can  be 
formed  even  in  the  outer  electrolyte  and  vice  versa  [and 
hence]  the  matter  of  position  is  under  complete  control."  l 

POTASSIUM  DIURANATE. 

When  a  uranyl  salt  is  treated  with  caustic  potash,  a  gelat- 
inous, yellow  precipitate  is  formed  which  is  a  derivative,  not 
of  the  normal  hydroxide  UO2(OH)2,  but  of  its  anhydride 

U02(OH)X 
^ 


The  composition  of  the  membrane  investigated  is  expressed 
by  the  formula  |JQ  (OK)/°' 


Nearly  all  of  the  membranes  studied  in  this  laboratory  which 
have  given  the  most  satisfactory  results  have  been  those  formed 
upon  the  interior  surface  of  the  cell.  From  a  consideration  of 
the  high  atomic  weight  of  uranium,  it  seemed  probable  that  the 
uranyl  ion  would  move  much  more  slowly  than  the  hydroxyl 
ion  of  the  caustic  potash,  and  that  the  solution  of  the  alkali 
should,  therefore,  surround  the  cell  which  was  filled  with  the 
uranyl  acetate.  The  electrode  within  the  cup  would  then  be 
made  the  anode. 

A  small  cell  was  accordingly  filled  with  a  tenth  normal  solu- 
tion of  uranyl  acetate  and  immersed  in  a  hundredth  normal 
solution  of  caustic  potash.  With  an  electromotive  force  of 
twelve  volts  the  resistance  rose  in  twenty  minutes  to  600  ohms. 
The  voltage  was  then  increased  to  46,  but  as  the  membrane 
showed  signs  of  being  ruptured  it  was  reduced  to  34  and  fifteen 
minutes  later  to  18.5.  The  resistance  at  this  time  was  438 
ohms,  and  as  it  fell  during  the  next  twenty  minutes  to  325, 
the  circuit  was  broken  and  the  cell  removed  for  examination. 
Its  exterior  surface  was  found  to  be  covered  with  a  yellow, 

1J.  P.  Coony,  Dissertation,  Johns  Hopkins  University  (1903),  p.  11. 


16  A    STUDY    OF    SEMIPERMEABLE    MEMBRANES. 

rather  granular  precipitate  unevenly  distributed  and,  for  the 
most  part,  quite  easily  detachable.  The  cell  was,  accordingly, 
prepared  for  a  second  trial  by  dissolving  the  precipitate  in 
acetic  acid  which  was  forced  through  the  cell  wall  by  means  of 
a  110-volt  current.  The  high  resistance  which  was  finally 
developed  indicated  the  almost  complete  removal  of  the  acid. 

The  cell  was  then  filled  with  a  hundredth  normal  solution 
of  the  alkali  and  immersed  in  a  tenth  normal  solution  of  the 
uranyl  salt  into  which  the  anode  dipped.  The  usual  initial 
voltage  of  1 2  was  increased  at  the  end  of  the  first  half  hour  to 
20,  where  it  remained  for  two  hours  and  twenty  minutes.  The 
resistance  reached  625  ohms.  During  the  next  two  hours  and 
forty  minutes  the  electromotive  force  was  raised  to  57.5  volts, 
but  as  the  resistance  began  to  decrease,  the  cup  was  removed, 
washed,  filled  with  strong  alcohol  and  immersed  in  water.  As 
no  indication  of  osmotic  pressure  was  manifest  on  the  following 
morning,  the  stopper  was  removed  and  the  interior  of  the  cup 
was  examined.  The  precipitate,  as  in  the  previous  case,  was 
granular  and  could  be  easily  removed  from  the  upper  half  of 
the  cell  by  rubbing  with  the  finger. 

The  membrane  seems  to  be  weak.  In  another  trial  with  a 
different  cup,  the  precipitate  was  formed  within  the  cell  wall 
instead  of  on  its  surface  and  yet  in  spite  of  the  support  which 
it  received  in  this  case,  the  resistance  decreased  from  4,570  to 
3,086  ohms  when  the  electromotive  force  was  raised  from  96 
to  108  volts. 

On  account  of  the  unpromising  character  of  the  diuranate 
precipitate,  a  more  thorough  investigation  of  the  phenomena 
which  have  been  described  above  was  not  undertaken.  It  is, 
however,  not  impossible  that  under  different  conditions  the 
membrane  may  be  deposited  in  a  satisfactory  manner. 

STANNOUS  HYDROXIDE. 

When  a  solution  of  stannous  chloride  slightly  acidified  with 
hydrochloric  acid  is  treated  with  caustic  potash,  a  white,  floe- 


STANNOUS    HYDROXIDE.  17 

culent  precipitate  is  formed  which  dissolves  in  excess  of  the 
alkali.     This  precipitate  is  stanuous  hydroxide. 

Since  the  chloride  of  tin  was  used  for  the  deposition  of  this 
substance,  a  platinum  anode  was  out  of  the  question  and  was 
substituted  by  one  made  of  pure  sheet  tin,  large  enough  to  sur- 
round the  bottle-shaped  cell  in  the  walls  of  which  the  mem- 
brane was  deposited.  The  alkali  used  was  caustic  potash. 

The  initial  electromotive  force  of  1 4  volts  was  increased 
during  two  hours  to  60 ;  the  resistance  rose  to  220  ohms. 

On  the  following  day  an  attempt  was  made  by  reenforce- 
ment,  to  obtain  a  membrane  which  would  withstand  a  higher 
voltage.  The  maximum  resistance  of  511  ohms  was  obtained 
by  using  a  current  having  an  electromotive  force  of  less  than 
60  volts. 

The  membrane  manifested  no  signs  of  osmotic  activity. 

A  week  later  the  cell  was  subjected  to  a  repetition  of  the 
same  treatment  except  that  the  voltage  of  the  current  was 
larger,  ranging  from  95  to  105.  That  this  electromotive  force 
was  too  high  was  shown  by  the  fact  that  at  the  end  of  two 
hours  the  resistance  was  only  269  ohms. 

The  results  were  more  encouraging  when  the  cell  was  set  up 
with  a  sugar  solution  in  the  usual  manner,  b>ut  the  rate  of 
delivery  was  so  slow  that  no  record  of  it  was  made. 

About  four  months  later  the  same  membrane  was  tried  again 
in  a  fresh  cell  of  the  same  type.  This  time  the  resistance  in- 
creased more  rapidly  and  in  two  hours  had  reached  about  700 
ohms  with  a  current  potential  of  99.5  volts.  This  looked 
promising,  but  only  until  experiment  proved  the  total  failure 
of  the  membrane  to  show  activity. 

The  cell  was  reenforced,  with  the  development  of  a  maxi- 
mum resistance  of  1,530  ohms,  the  electromotive  force  of  the 
current  being  104  volts. 

The  readiness  with  which  some  metals  form  saccharates  sug- 
gested the  idea  that  previous  failures  with  this  membrane 
might  have  been  due  to  the  action  of  sugar  upon  it.  Alcohol 


18  A    STUDY    OF    SEMIPERMEABLE    MEMBRANES. 

of  about  95  per  cent,  strength  was,  accordingly,  substituted  for 
the  sugar  and  the  cell  was  immersed  as  before,  in  water.  The 
delivery  in  three  days  was  53.7  cc.,  or,  in  periods  of  twenty- 
four  hours  each,  as  follows:  (1)  29.5  cc.,  (2)  18.8  cc.,  (3) 
5.4  cc. 

SILVER  COBALTICYANIDE. 

Silver  cobalticyanide  is  precipitated  from  a  solution  of  silver 
nitrate  by  potassium  cobalticyanide,  as  a  white,  flocculent  sub- 
stance which  is  insoluble  in  acetic  acid  but  is  easily  decom- 
posed by  caustic  potash. 

One  of  the  large  cups  was  selected  for  the  testing  of  a  mem- 
brane of  this  composition.  It  was  filled  with  a  solution  of  the 
alkali  cobalticyanide  and  immersed  in  a  solution  of  silver 
nitrate  into  which  the  anode  dipped.  The  initial  voltage  of  9 
was  increased  during  forty-five  minutes  to  24  where  it  remained 
for  about  two  and  one-half  hours.  As  the  maximum  resistance 
of  74  ohms  decreased  during  the  last  hour  to  72  ohms,  the  cir- 
cuit was  broken  and  the  cell  was  removed  from  the  nitrate 
solution  and  emptied. 

The  interior  surface  was  found  to  be  covered  with  a  gray 
precipitate  consisting,  probably,  of  the  oxide  of  silver  formed 
by  the  potassium  hydroxide  which  collected  around  the  cathode 
during  the  deposition  of  the  membrane. 

This  accumulation  of  alkali  can  be  prevented  either  by  fre- 
quently renewing  the  potassium  cobalticyanide  solution  or  by 
adding  to  it  a  little  acetic  acid  which  neutralizes  the  alkali  as 
soon  as  formed. 

The  former  method  having  been  unsuccessfully  tried  in  the 
first  attempt  to  form  the  membrane,  the  second  method  was 
employed  in  an  eifort  to  reenforce  it.  A  little  dilute  acetic  acid 
was  added  to  the  cobalticyanide  solution  in  the  cell,  but  although 
the  resistance  rose  to  100  ohms,  the  membrane  proved  to  be  in- 
active. 

When  the  cell  was  broken,  a  very  regular,  gray  membrane 
was  found  within  the  cell  wall. 


ZINC    COBALTICYANIDE.  19 

In  view  of  the  unpromising  character  of  this  precipitate,  fur- 
ther experimentation  upon  it  was  abandoned. 

MANGANESE  COBALTICYANIDE. 

Manganese  cobalticyanide  is  a  white,  gelatinous  substance 
which  is  easily  decomposed  by  caustic  potash.  For  the  forma- 
tion of  a  membrane  of  this  composition,  solutions  of  manganese 
sulphate  and  potassium  cobalticyanide  were  employed.  One  of 
the  bottle-shaped  cells  containing  the  potassium  salt  was  im- 
mersed in  the  sulphate  solution  which  also  contained  the  platinum 
anode.  The  initial  voltage  of  10  was  increased  to  22  an  hour 
and  a  quarter  after  closing  the  circuit.  Although  it  remained 
here  for  the  next  four  hours  the  highest  resistance  obtainable 
was  only  87  ohms. 

In  spite  of  the  unpromising  behavior  of  this  cell,  judging  by 
the  comparatively  small  resistance  offered  to  the  current,  by  the 
membrane,  it  was  filled  as  usual  with  a  normal  solution  of  cane 
sugar  and  set  up  in  the  constant  temperature  bath  which  was 
kept  at  28°.  In  18|  days  the  cell  had  delivered  105  cc. 

It  is  quite  possible  that  if  acetic  acid  had  been  added  to  the 
cobalticyanide  solution  within  the  cup,  the  membrane  would 
have  proved  more  efficient. 

ZINC  COBALTICYANIDE. 

When  any  soluble  zinc  salt  is  treated  with  a  solution  of  potas- 
sium cobalticyanide,  white,  gelatinous  zinc  cobalticyanide  is  pre- 
cipitated. It  is  soluble  in  the  caustic  alkalis  but  insoluble  in 
acetic  acid. 

The  zinc  cobalticyanide  membrane  was,  like  most  of  the 
membranes  already  described,  deposited  in  one  of  the  large 
cups.  The  zinc  salt  employed  was  the  sulphate  and  in  this 
solution,  which  surrounded  the  cell,  the  zinc  anode  was  im- 
mersed. No  acetic  acid  was  added  to  the  potassium  cobalti- 
cyanide solution  in  the  cup. 

In  the  first  trial,  the  maximum  resistance  offered  to  the  cur- 


20 


A    STUDY    OF   SEMIPERMEABLE    MEMBRANES. 


rent,  which  at  no  time  had  an  electromotive  force  of  more  than 
62  volts,  was  392  ohms.  When  higher  voltages  were  employed 
the  membrane  showed  unmistakable  signs  of  being  ruptured  and 
it  was  only  by  using  great  care  and  after  passing  the  current 
for  about  six  hours,  that  a  membrane  was  built  up  capable  of 
withstanding  a  current-pressure  of  even  62  volts. 

The  cell  was  filled  with  a  normal  sugar  solution  and  im- 
mersed in  water  kept  at  28°.  The  following  table  gives  the 
results  of  observations  made  on  the  activity  of  this  membrane. 
Unless  otherwise  indicated,  the  readings  were  made  every 
twenty-four  hours. 

TABLE  II. 


Time. 

Delivery  in  cc. 

Time. 

Delivery  in  cc. 

12  :  10  p.  in. 

5 

4.3 

9  :  55  a.  m. 

6.0 

6 

4.2 

1 

5.5 

71 

8.2 

2 

4.5 

82 

13.3 

31 

10.0 

9 

4.8 

4 

5.0 

10 

4.4 

Total  time  of  delivery  14  days,  22^  hours. 
Total  volume  of  solution  delivered,  70.2  cc. 

A  second  trial  of  the  same  membrane  was  made  in  a  fresh 
cup  in  the  same  manner  as  that  just  described,  except  that  a 
few  cubic  centimeters  of  dilute  acetic  acid  were  added  to  the 
solution  of  cobalticyanide  in  the  cell  for  the  purpose  of  neu- 
tralizing the  alkali  which  was  constantly  being  formed  at  the 
cathode.  The  higher  resistance  offered  to  the  current  in  this 
case  is  to  be  attributed  either  to  this  addition  of  acid  or  to  the 
fact  that  the  second  cup  was  of  better  quality  than  the  first. 

During  the  course  of  two  hours  the  electromotive  force  of 
the  current  was  raised  from  11.5  to  51.5  volts,  where  it  was 
kept  for  about  half  an  hour.  The  highest  resistance  obtained 
was  706  ohms. 

This  cell  was  set  up  in  the  usual  manner  with  a  normal 
sugar  solution  which  was  maintained  at  a  temperature  of  28°. 

1  Forty-eight  hour  interval  between  readings. 

2  Seventy-two  hour  interval  between  readings. 


CADMIUM    COBALTICYANIDE. 


21 


A  record  of  the  rate  of  delivery  of  this  cell  is  given  in  Table 
III.  Unless  otherwise  indicated  the  readings  were  made 
every  twenty-four  hours. 

TABLE  III. 


Time. 

Delivery  in  cc. 

Time. 

Delivery  in  cc. 

6  :  00  p.  m. 

5 

9.5 

9  :  55  a.  m. 

9.7 

6 

9.5 

1 

8.8 

71 

26.5 

2 

9.5 

8 

7.5 

3 

9.5 

9 

6.7 

4 

9.5 

Total  time  of  delivery  llf  days. 

Total  volume  of  solution  delivered,  106.7  cc. 

CADMIUM  COBALTICYANIDE. 

Potassium  cobalticyanide  precipitates  from  a  solution  of  a 
cadmium  salt,  white,  gelatinous  cadmium  cobalticyanide  which 
is  insoluble  in  acetic  acid. 

For  the  deposition  of  this  membrane  in  one  of  the  large  cups 
a  fifth  normal  solution  of  cadmium  sulphate  and  a  tenth  nor- 
mal solution  of  the  alkali  cobalticyanide  were  used.  Both 
electrodes  were  of  platinum  ;  the  outer  one  was  made  the 
anode,  as  usual.  The  voltage  of  the  current  was  gradually 
increased  from  10  to  52  ;  the  final  resistance  was  578  ohms. 

The  cell  was  filled  with  a  normal  sugar  solution  and  set  up 
in  a  bath  in  which  a  constant  temperature  of  35°  was  main- 
tained. 

Table  IV.  contains  a  record  of  the  number  of  cubic  centi- 
meters delivered  daily  for  a  period  of  six  days. 

TABLE  IV. 


Delivery  in  cc. 

Delivery  in  cc. 

1 

2 
3 

12.3 
12.5 
11.2 

4 
5 
6 

10.3 
9.0 
10.2 

Total  volume  of  solution  delivered,  65.5  cc. 
1  Seventy-two  hour  period. 


22  A  STUDY  OF  SEMIPERMEABLE  MEMBRANES. 

MERCUROUS  FERROCYANIDE. 

An  attempt  was  made  to  form  a  membrane  of  mercurous 
ferrocyanide  in  one  of  the  bottle  cells,  using  as  the  outer  elec- 
trolyte a  solution  of  mercurous  nitrate  to  which  enough  of  the 
metal  was  added  to  cover  the  bottom  of  the  beaker. 

The  exterior  electrode  was,  as  usual,  made  the  anode.  Dur- 
ing a  period  of  forty  minutes  the  electromotive  force  was  in- 
creased from  11  to  74.5  volts,  but  when  it  was  raised  to  110 
the  resistance  decreased  from  784  to  733  ohms  and  the  circuit 
was  therefore  broken. 

The  cell  was  set  up  in  the  usual  manner,  but  as  there  was 
no  evidence  of  osmotic  pressure,  it  was  subjected  for  the  second 
time  to  the  membrane-forming  process.  The  current  was 
passed  for  45  minutes,  practically  all  of  this  time  at  a  voltage 
of  108,  but  although  the  resistance  rose  to  1,235  ohrns,  the 
membrane  still  exhibited  no  activity. 

Only  one  cell  was  used  in  testing  this  membrane  and  the 
evidence  is,  therefore,  not  sufficient  to  justify  the  conclusion 
which  would  otherwise  be  drawn  from  the  results  of  the  exper- 
iment described  above. 

This  membrane  illustrates  in  a  striking  way  the  fact  that  the 
magnitude  of  the  resistance  of  the  membrane  is  not  a  measure 
of  its  osmotic  activity. 

SILVER  FERROCYANIDE. 

Silver  ferrocyanide  like  the  cobalticyanide  is  precipitated 
from  silver  nitrate  solutions  as  a  white,  curdy  mass,  easily  de- 
composed by  alkalis,  but  insoluble  in  acetic  acid. 

A  large  cup  was  used  for  the  testing  of  this  substance. 
Before  filling  the  cell  with  the  ferrocyanide  solution,  15  cc.  of 
acetic  acid  were  introduced  and  in  every  100  cc.  of  the  solu- 
tion subsequently  used  there  were  2  cc.  of  this  acid. 

The  highest  voltage  employed  was  only  12.  At  one  time, 
after  the  current  had  been  passing  for  about  half  an  hour,  the 
voltage  was  raised  to  60  but  the  immediate  decrease  in  resist- 


STANNOUS    FERROCYANIDE.  23 

ance  showed  that  the  membrane  was  being  ruptured,  and  a  re- 
turn was  made  to  the  original  12  volts.  The  membrane  did 
not  adhere  to  the  interior  surface  on  which  it  was  deposited, 
and  the  resistance  never  rose  above  86  ohms.  Metallic  silver 
was  precipitated  in  the  nitrate  solution  outside  the  cup. 

The  membrane  gave  only  slight  evidence  of  osmotic  activity 
when  the  cell  containing  it  was  filled  with  a  sugar  solution  and 
immersed  in  water. 

While  other  attempts  made  in  this  laboratory  to  prepare  an 
osmotically  active  membrane  of  this  composition  have  not  met 
with  the  success  which  might  reasonably  be  expected  from  a 
consideration  of  the  appearance  of  the  precipitate,  it  is  quite 
possible  that  under  conditions  as  yet  unknown,  both  the  cobalt- 
icyanide  and  ferrocyanide  of  silver  may  prove  to  be  suitable  for 
the  formation  of  semipermeable  membranes. 

STANNOUS  FERROCYANIDE. 

Stannous  ferrocyanide  is  precipitated  as  a  white,  flocculent 
substance  from  solutions  of  potassium  ferrocyanide  and  slightly 
acidified  stannous  chloride.  It  is  insoluble  in  dilute  acetic  acid, 
but  is  soluble  in  hydrochloric  acid  and  in  an  excess  of  alkali. 

The  stannous  ferrocyanide  membrane  was  deposited  in  one 
of  the  bottle-shaped  cells,  the  only  modification  in  the  appar- 
atus ordinarily  employed  being  that  the  large  anode  which  sur- 
rounded the  cell  was  of  tin  instead  of  platinum.  The  maxi- 
mum resistance  of  1,170  ohms  was  reached  in  two  hours  and 
twenty-five  minutes,  with  a  final  current  potential  of  103  volts. 

The  cell  was  filled  with  a  normal  sugar  solution  and  immersed 
in  water  at  the  temperature  of  the  room.  In  42  days  the  cup 
delivered  409  cc. 

Although  still  active,  the  membrane  was  reenforced  in  the 
usual  manner.  The  highest  resistance  obtained  was  2,120 
ohms,  using  a  current  with  an  electromotive  force  of  127  volts. 

An  attempt  was  then  made  to  determine  the  relation  at  con- 
stant temperature,  between  the  rate  at  which  the  solution  was 


24 


A    STUDY    OF    SEMIPERMEABLE    MEMBRANES. 


delivered  from  the  cell  and  the  concentration  of  the  sugar 
solution  within. 

The  results  of  observations  made  with  this  end  in  view  are 
presented  in  Table  V.  The  temperature  of  the  bath  in  which 
the  cell  was  immersed  was  kept  at  28°.  Capacity  of  cell  186  cc. 

TABLE  V. 

Column  I.  Number  of  cubic  centimeters  delivered  in  periods  of  12  hours 
each. 

Column  II.     Number  of  grams  of  sugar  in  1  cc.  of  solution  delivered. 

Column  III.     Mean  number  of  grams  of  sugar  in  1  cc.  solution  in  cell. 

Column  IV.  Ratio  of  concentration  of  solution  delivered,  to  mean  con- 
centration of  solution  in  cell. 

Column  V.     Rate  of  delivery  in  cubic  centimeters  per  hour. 

Column  VI.     Ratio  of  concentration  of  cell  contents  to  rate  of  delivery. 


I 

II 

in 

IV 

v 

VI 

1 

2 
3 

4 
5 

24.2 
18.0 
15.8 
14.6 
13.2 

0.30054 
0.26525 
0.24604 
0.22853 
0.21267 

0.32443 
0.29204 
0.26876 
0.24934 
0.23282 

0.926 
0.908 
0.915 
0.917 
0.913 

2.02 
1.50 
1.32 
1.22 
1.10 

0.1606 
0.1947 
0.2036 
0.2044 
0.2117 

Total  volume  of  solution  delivered,  85.8  cc. 
Total  time  of  delivery  2£  days. 

The  figures  in  column  n.  were  obtained  by  determining  the 
strength  of  the  volumes  of  solution  given  in  column  I.  by 
means  of  Fehling's  solution. 

The  average  concentration  of  the  cell  contents  during  the 
period  required  for  the  delivery  of  each  of  these  volumes,  was 
calculated  on  the  assumption  that  the  membrane  was  impervious 
to  a  cane  sugar  solution,  that  is,  that  none  of  the  sugar  leaked 
through  the  walls  of  the  cell  into  the  surrounding  water.  This 
assumption  was  later  proved  to  be  incorrect  and  other  workers  l 
in  this  laboratory  have  found  that  membranes  of  other  sub- 
stances behave  in  a  similar  manner. 

It  is  obvious  that  if  the  rate  of  delivery  is  proportional,  at 

JB.  F.  Carver,  Dissertation,  Johns  Hopkins  University  (1903),  pp.  21,  25, 
26,  etc.;  J.  P.  Coony,  Dissertation,  Johns  Hopkins  University  (1903),  p.  26, 
et  seq. 


URANYL    FERROCYANIDE.  25 

constant  temperature,  to  the  concentration  of  the  solution  within 
the  cell,  the  ratio  of  the  numbers  representing  these  values  should 
be  a  constant.  That  this  is  not  the  case,  on  the  basis  of  the 
calculation  mentioned  above,  can  be  seen  from  an  inspection  of 
column  vi.,  but,  as  will  be  shown  later,  when  the  amount  of 
sugar  which  leaked  through  the  membrane  was  determined  and 
the  necessary  correction  introduced  into  the  calculation  of  the 
strength  of  the  cell  contents,  the  value  of  the  ratio  approached 
a  constant. 

Column  iv.  gives  the  ratio  of  the  concentration  of  the  solu- 
tion delivered  in  each  period  of  twelve  hours  to  the  average 
concentration  of  the  cell  contents  for  the  same  period  of  time. 
It  will  be  noticed  that  the  highest  value  of  this  ratio  expressed 
in  percentages  is  92.6,  which  means  that  the  concentration  of 
the  delivered  liquid  is  less  by  at  least  7.4  per  cent,  than  would 
be  expected.  The  only  obvious  explanation  of  this  fact  is  that 
the  water  which  enters  the  cell  through  the  membrane  glides 
up  the  wall  toward  the  top,  giving  in  that  region  a  solution 
which  is  more  dilute  than  that  in  the  interior  portions  of  the 
liquid.  Although  the  values  of  the  concentrations  presented  in 
column  in.  are  undoubtedly  too  high,  owing  to  the  undeter- 
mined amounts  of  sugar  which  must  have  leaked  through  the 
membrane,  the  error  in  the  calculations  arising  from  this  source 
can  scarcely  have  been  great  enough  to  account  for  this  dis- 
crepancy of  more  than  7  per  cent. 

Data  concerning  this  point  are  presented  in  Table  VII.  on 
page  30  and  will  be  discussed  in  connection  with  facts  brought 
out  by  a  study  of  the  uranyl  ferrocyanide  membrane. 

URANYL  FERROCYANIDE. 

A  brownish  red  precipitate  of  uranyl  ferrocyanide  is  formed 
when  a  solution  of  uranyl  acetate  is  treated  with  potassium 
ferrocyanide.  It  is  insoluble  in  dilute  acetic  acid  but  is  easily 
dissolved  by  warm  dilute  hydrochloric  acid.  It  is  easily  de- 
composed by  sodium  and  potassium  hydroxide  and  for  this 


26  A    STUDY    OF    SEM1PEJRMEABLE    MEMBRANES. 

reason  care  must  be  taken  to  prevent  an  accumulation  of  alkali 
around  the  cathode  during  the  deposition  of  the  membrane. 
In  the  experiment  to  be  described  this  was  accomplished  by 
frequently  renewing  the  potassium  ferrocyanide  solution. 

The  first  uranyl  ferrocyanide  membrane  was  deposited  in 
one  of  the  small  cups  which  was,  accordingly,  immersed  in  a 
solution  of  uranyl  acetate  containing  the  anode  and  filled  with 
a  solution  of  potassium  ferrocyanide. 

The  electromotive  force  of  the  current  which  was  used  at 
first  was  29  volts.  This  was  increased  to  96  volts  during  the 
first  hour  and  forty  minutes  at  the  end  of  which  period  the  re- 
sistance was  9,600  ohms.  During  the  next  half  hour  the  voltage 
was  raised  to  109,  and  the  maximum  resistance  of  10,850  ohms 
was  reached. 

When  the  cell  was  filled  with  an  approximately  normal  sugar 
solution  and  immersed  in  a  beaker  of  water  standing  on  the 
floor,  the  liquid  rose  in  the  capillary  tubing  to  a  height  of  about 
12  feet.  At  this  point  connection  was  made  by  means  of  a  tube 
bent  to  two  right  angles,  with  a  test-tube  which  received  the 
overflow.  In  this  way  about  10  cc.  of  the  sugar  solution 
were  collected  during  the  next  few  days. 

The  cell  was  broken  and  found  to  be  covered  on  the  interior 
surface  with  a  membrane  which  did  not  at  all  resemble  in  color 
the  dark  red  precipitate  of  the  uranyl  ferrocyanide  but  was 
pale  yellow,  with  traces  of  green  and  blue.  Since  all  mem- 
branes of  this  composition,  so  far  as  observed,  suffered  this 
change  of  color  when  allowed  to  stand  in  contact  with  a  sugar 
solution,  it  seems  probable  that  they  are  decomposed  by  it. 

A  membrane  of  the  same  composition  was  deposited  in  one 
of  the  bottle-shaped  cells.  The  electromotive  force  at  the  be- 
ginning was  7  volts.  In  one  and  one-half  hours  the  resistance 
had  reached  686  ohms  and  about  three  hours  later,  with  a 
voltage  of  108,  the  maximum  resistance  of  1,009  ohms  was 
obtained. 

The  activity  of  this  membrane  was  tested  according  to  the 


URANYL    FEKKOCYANIDE.  27 

second  method  already  described,  using  a  sugar  solution  which 
was  about  normal.  During  the  first  sixteen  days  the  cell  de- 
livered 227  cc.;  the  total  delivery  in  42  days  was  418  cc. 

No  attempt  to  investigate  the  relation  between  concentration 
and  rate  of  delivery  was  possible  as  long  as  the  cell  was  sub- 
jected to  fluctuations  of  temperature  which  often  amounted, 
during  a  period  of  twenty-four  hours,  to  15°. 

The  cell  was  emptied,  thoroughly  rinsed  with  water  and 
about  a  week  later  was  set  up  without  reinforcement  of  the 
membrane,  in  the  same  manner  as  before,  except  that  the  water 
in  which  the  cell  was  immersed  was  kept  at  a  constant  tempera- 
ture of  28°.  Under  these  conditions  the  cell  delivered  142 
cc.  in  nine  days. 

Although  the  membrane  still  showed  activity  it  was  reen- 
forced  in  the  manner  previously  explained,  before  it  was  set 
up  for  the  third  time.  The  voltage  of  the  current  was  increased 
more  rapidly  than  was  the  case  when  the  membrane  was  first 
deposited  and  the  current  was  passed  for  only  about  half  an 
hour.  During  this  short  period  of  time  the  voltage  was  raised 
from  11  to  103  and  the  maximum  resistance  of  1,716  ohms 
was  reached. 

The  results  of  observations  made  upon  the  osmotic  activity 
of  this  membrane  are  presented  in  Table  VI. 

The  cell,  which  had  a  capacity  of  178  cc.,  was  filled  with  a 
solution  containing  279.75  grams  of  sugar  per  liter,  as  deter- 
mined by  Fehling's  solution. 

The  bath  in  which  the  cell  was  placed  was  maintained  at  a 
temperature  of  28°. 

The  figures  in  column  n.  were  obtained  from  a  determina- 
tion, by  means  of  the  Mohr-Westphal  balance,  of  the  specific 
gravity  of  the  volumes  of  solution  given  in  column  I. 

A  comparison  of  columns  u.  and  in.  shows  that  here  also, 
as  was  the  case  in  Table  V.,  the  mean  concentration  of 
the  cell  contents  for  a  specified  time,  if  the  leakage  of  sugar 
was  not  taken  into  account,  was  always  greater  than  the 


28 


A    STUDY   OF    SEMIPERMEABLE    MEMBRANES. 


concentration  of  the  solution  delivered  during  the  same  period 

of  time. 

TABLE  VI. 

Column  I.  Number  of  cubic  centimeters  delivered  in  12-hour  periods 
(except  as  otherwise  indicated). 

Column  II.     Number  of  grams  of  sugar  in  1  cc.  of  solution  delivered. 

Column  III.     Mean  number  of  grams  of  sugar  in  1  cc.  of  solution  in  cell. 

Column  IV.  Ratio  of  concentration  of  solution  delivered,  to  mean  concen- 
tration of  solution  in  cell. 

Column  V.     Rate  of  delivery  in  cubic  centimeters  per  hour. 

Column  VI.     Ratio  of  concentration  of  cell  contents  to  rate  of  delivery. 


I 

II, 

in 

IV 

v 

VI 

1 

43.0 

0.22255            0.25287 

0.880 

3.58 

0.0706 

2 

32.1 

0.18252            0.20953 

0.871 

2.68 

0.0782 

3 

27.7 

0.15922            0.18068           0.881 

2.31 

0.0782 

4 

24.0 

0.13911           0.15892 

0.875 

2.00 

0.0794 

£ 

20.7 

0.12499           0.14227          0.879 

1.73 

0.0822 

6 

17.9 

0.11262            0.12934 

0.877 

1.49 

0.0865 

71 

31.0 

0.09860 

0.11509          0.857 

1.29 

0.0892 

8 

13.8 

0.08492            0.10321 

0.823 

1.15 

0.0897 

9 

11.8 

0.07879           0.09311 

0.846 

0.98 

0.0950 

101 

21.0 

0.07336 

0.09037 

0.812 

0.88 

0.103 

II1 

17.2 

0.06657 

0.08283 

0.804 

0.72 

0.115 

121 

16.5 

0.06347 

0.07668 

0.828 

0.69 

0.111 

Total  volume  of  solution  delivered,  276.7  cc. 
Total  time  of  delivery,  8  days. 

By  an  inspection  of  column  iv.,  which  contains  the  ratios 
of  the  numbers  in  column  n.  to  those  in  column  in.,  it  will 
be  seen  that  the  concentration  of  the  delivered  liquid  was  less 
by  at  least  12  per  cent,  than  would  be  expected. 

It  is  obvious  that  a  correction  for  the  leakage  of  sugar 
through  the  membrane  would  reduce  the  values  of  the  mean 
concentrations  of  the  cell  for  specified  times,  as  presented  in 
column  in.,  and  that  consequently  the  numbers  given  in 
column  iv.  would  approach  more  nearly  100  per  cent. 

As  was  stated  in  the  discussion  of  Table  V.,  the  other  cause 
of  the  discrepancy  between  the  values  of  the  concentration  of 
the  delivered  solution  and  the  mean  concentration  of  the  cell 
contents,  was  thought  to  be  the  incomplete  diffusion  of  the 
water  which  entered  the  cell. 

1  Twenty-four  hour  periods. 


URANYL    FERROCYANIDE.  29 

Column  vi.  gives  the  ratio  of  the  average  concentration  of 
the  cell  contents  for  a  specified  time  to  the  rate  of  delivery  of 
the  cell  for  the  same  period  of  time.  Here  also  as  was  the 
case  in  Table  V.,  the  ratio  does  not  have  the  constant  value 
which  it  would  possess  if  the  rate  of  delivery  were  proportional 
to  the  concentration  of  the  solution  in  the  cell.  It  will  further 
be  noticed  that  in  both  Table  V.  and  Table  VI.,  the  value  of 
the  ratio  increases  from  the  top  to  the  bottom  of  the  column. 

This  increase  can  be  satisfactorily  accounted  for  by  a  consid- 
eration of  the  fact  that  if  the  cell  had  suffered  a  constant 
decrease  in  concentration  due  to  leakage  of  sugar  through  the 
membrane,  the  error  produced  in  the  calculations  of  the  con- 
centrations as  given  in  column  in.  would  be  cumulative  and 
would  tend  to  produce  the  increase  in  the  values  of  the  ratios 
found  in  column  vi. 

The  membrane  in  this  cup  was  reenforced  for  the  last  time 
on  April  20.  The  maximum  resistance  obtained  with  a  cur- 
rent of  104  volts  was  2,600  ohms. 

With  a  view  to  ascertaining  more  exactly  the  average  con- 
centration of  the  contents  of  the  cell  for  any  period  of  time,  it 
became  necessary  to  determine  the  amount  of  sugar  which  had 
leaked  through  the  membrane  during  this  time  as  well  as  that 
which  had  been  collected  in  the  gas  measuring-tube.  The  sum 
of  these  two  quantities  would  be  equal  to  the  total  decrease  in 
the  concentration  of  the  cell. 

The  only  other  change  which  was  made  in  this  experiment 
consisted  in  the  use  of  a  stirrer  which  kept  the  liquid  in  the 
cell  in  constant  motion.  A  piece  of  glass  tubing  3  or  4  cm.  in 
length  and  of  about  the  same  diameter  as  the  neck  of  the  cell, 
was  provided  with  a  horizontal  side  tube,  the  outer  end  of 
which  was  bent  down  for  the  delivery  of  the  liquid  into  the 
measuring-tubes.  Through  the  vertical  tube  which  was  joined 
to  the  neck  of  the  cell,  was  passed  a  silver-plated  steel  rod,  to 
the  lower  end  of  which  were  fastened  two  cross-pieces  of  plati- 
num foil  shaped  like  the  blades  of  a  propeller.  This  stirrer, 


30 


A    STUDY    OF   SEMIPERMEABLE    MEMBRANES. 


which   on   preliminary  trial   proved   to   be  very  efficient,  was 
driven  by  a  small  electric  motor. 

The  results  of  the  last  observations  which  were  made  in 
connection  with  this  cell  are  presented  in  Table  VII. 

The  concentration  of  the  sugar  solution  used  in  filling  the 
cup,  as  determined  by  Fehling's  solution,  was  337.9  grams  per 
liter.  The  temperature  of  the  bath  in  which  the  cell  was  set 
up  ranged  from  27°. 7  to  31°. 2.  Capacity  of  cell  with  stirrer 
in  place  194.8  cc. 

TABLE  VII. 

Column  I.     Volume  of  delivered  solution  in  cubic  centimeters. 

Column  II.     Number  of  grams  of  sugar  in  1  cc.  of  solution  delivered. 

Column  III.  Mean  number  of  grams  of  sugar  in  1  cc.  of  solution  in  cell, 
(corrected  for  leakage). 

Column  IV.  Ratio  of  concentration  of  solution  delivered,  to  mean  con- 
centration of  solution  in  cell. 

Column  V.     Rate  of  delivery  in  cubic  centimeters  per  hour. 

Column  VI.     Ratio  of  concentration  of  cell  contents  to  rate  of  delivery. 

Column  VII.     Number  of  grams  of  sugar  in  water  surrounding  cell. 


I 

II 

III 

IV 

-    V' 

VI 

VII 

1 

22.  41 

0.30282 

0.32409 

0.934 

3.70 

0.0876 

0.232 

2 

31.  82 

0.24198 

0.28571 

0.935 

2.65 

0.108 

0.285 

3 

27.3 

0.23094 

0.24818 

0.931 

2.28 

0.109 

0.297 

4 

22.3 

0.20446 

0.21862 

0.935 

1.86 

0.118 

0.357 

5 

20.7 

0.17834 

0.19575 

0.911 

1.73 

0.113 

0.3005 

6 

18.0 

0.15931 

0.17738 

0.898 

1.50 

0.118 

0.3005 

7 

17.0 

0.14591 

0.16119 

0.905 

1.41 

0.114 

0.489 

8 

15.7 

0.13375 

0.14597 

0.916 

1.31 

0.111 

0.519 

9 

39.  43 

0.11069 

0.12497 

0.886 

1.09 

0.115 

1.029 

10 

11.0 

0.09413 

0.10581 

0.889 

0.92 

0.115 

0.315 

11 

21.74 

0.08174 

0.09804 

0.834 

0.90 

0.109 

0.627 

12 

19.5 

0.06963 

0.08708 

0.800 

0.81 

0.107 

0.511 

13 

18.6 

0.77 

14 

15.3 

0.64 

15 

14.0 

0.58 

16 

12.6 

0.52 

17 

11.9     1 

0.50 

Total  volume  of  solution  delivered,  339.2  cc. 
Total  time  of  delivery  13|  days. 

1  Six  hour  period. 

2  Cell  contents  not  stirred. 

3  Thirty-six-hour  period . 

4  (!!)-( 17)  twenty-four-hour  periods. 

5  Estimated. 


URANYL    FERROCYANIDE.  31 

Attention  has  already  been  called  to  the  fact  that  according 
to  the  figures  presented  in  column  vi.  of  Tables  V.  and  VI., 
the  ratio  of  the  average  concentration  of  the  cell  for  a  specified 
period  of  time,  to  the  rate  of  delivery  for  the  same  period,  does 
not  approach  a  constant  but  that  there  is,  instead,  a  continuous 
increase  in  the  value  of  those  ratios. 

The  effect  of  a  determination  of  the  leakage  of  the  cell  is 
made  apparent  in  column  vi.  of  Table  VII.  With  the  excep- 
tion of  (1)  these  numbers  approach  a  constant  lying  somewhere 
between  0.107  and  0.118. 

The  results  presented  in  column  iv.  of  the  same  table  are 
not  as  satisfactory.  From  a  consideration  of  the  efficiency  of 
the  stirrer  it  seems  impossible  to  believe  that  the  water  which 
constantly  entered  the  cell  was  not  thoroughly  diffused  through- 
out the  solution  within,  and  yet  the  figures  seem  to  show  that 
this  was  not  the  case  but  that,  as  before,  the  contents  of  the 
cell  at  any  specified  time  was  more  concentrated  than  was  to 
be  expected.  The  continuous  decrease  in  the  percentages  from 
93.4  to  80.0  remains  unexplained.  Analogous  cases l  have  been 
met  with  in  this  laboratory. 

When  this  cup  was  broken,  the  membrane  was  found  to  be 
situated  on  the  interior  surface  and  to  be  of  the  bluish  yellow 
color  already  mentioned.  The  membrane  adhered  very  firmly 
to  the  cell  walls. 

CONCLUSIONS. 

The  investigation  described  in  the  preceding  pages  seems  to 
justify  the  following  conclusions  : 

1.  That  membranes  may   be   easily  deposited  by  the  elec- 
trolytic method  upon  or  within  the  walls  of  porous  clay  vessels 
separating  solutions  of  two  electrolytes  capable  of  forming  a 
precipitate. 

2.  That  the  number  of  semipermeable  membranes  capable 
of  formation  by  this  method  is  large. 

3.  That  of  the    membranes   investigated,  the  uranyl  ferro- 
1  B.  F.  Carver,  Dissertation,  Johns  Hopkins  University,  (1903),  pp.  26,  35. 


32  A    STUDY    OF    SEMIPEEMEABLE    MEMBRANES. 

cyanide  membrane  seems  to  be  the  most  promising  for  use  in 
the  measurement  of  high  osmotic  pressures. 

4.  That  when  cells  of  the  form  employed  in  this  work  are 
used,  the  liquid  delivered  during  any  period  of  time  is  less 
concentrated  than  the  average  contents  of  the  cell  during  the 
same  period. 

5.  That  the  magnitude  of  the  electrical  resistance  of  mem- 
branes deposited  within  or  upon  the  walls  of  the  imperfect  cells 
at  the  writer's  disposal,  is  not  a  measure  of  the  osmotic  activ- 
ity of  these  membranes,  or  of  their  suitability  for  use  in  the 
measurement  of  osmotic  pressure.     All  semi-permeable  mem- 
branes consisting  of  precipitated  chemical  compounds  are  weak, 
that  is,  easily  ruptured,  and  can  therefore  be  made  to  serve  for 
the  measurement  of  high  pressures  only  by  giving  them  a  most 
perfect  support  at  all  points. 

A  problem  which  has  been  foreseen  from  the  very  beginning 
of  the  work  of  Morse  and  Frazer  is  now  practically  the  only 
one  which  prevents  the  prosecution  of  the  investigation  of 
osmotic  pressure  phenomena  upon  a  quantitative  basis.  Until 
a  satisfactory  porous  cup  is  procured,  all  reliable  quantitative 
measurements  either  of  the  rate  of  endosmose  of  pure  solvent 
through  the  membrane  or  of  the  actual  pressures  developed 
within  the  cell,  is  impossible.  The  direction,  therefore,  which 
future  work  must  necessarily  take,  was  plainly  indicated,  and 
attention  was  turned  from  the  study  of  the  membranes  to  the 
construction  of  suitable  porous  vessels  in  which  to  deposit  them. 

The  prospects  of  early  success  in  this  direction  are  not  great, 
but  if  the  desired  end  is  eventually  attained,  the  contributions 
to  theoretical  chemistry  which  it  will  make  possible  will  more 
than  justify  the  expenditure  of  the  time  and  labor  which  its 
accomplishment  has  cost. 


II.  EXPERIMENTS    ON    THE    PREPARATION    OF 
POROUS  CUPS   SUITABLE  FOR   THE  MEAS- 
UREMENT OF  OSMOTIC  PRESSURE. 

The  three  essential  characteristics  of  cups  suitable  for  the 
measurement  of  high  pressures  have  already  been  mentioned, 
viz.,  strength,  the  greatest  compactness  and  uniformity  of  struc- 
ture compatible  with  the  requisite  porosity,  freedom  from  cavi- 
ties and  air-blisters.  Many  of  the  cells  obtained  from  the  pot- 
ters were  satisfactory  as  far  as  the  fineness  of  the  ingredients 
used  in  their  manufacture  was  concerned,  but  only  a  very  small 
percentage  of  them  approached  even  distantly  the  required 
standard  of  strength  and  uniform  density  of  texture.  The  only 
remaining  way  of  obtaining  porous  vessels  free  from  these  de- 
fects seemed  to  be  to  prepare  them  in  the  laboratory. 

Through  the  courtesy  of  D.  F.  Haynes  &  Son,  of  the  Ches- 
apeake Pottery  in  this  city,  four  varieties  of  clay  were  obtained 
from  their  works.  These  were  washed  by  elutriation  and  only 
the  finest  of  the  material  thus  separated  was  dried  and  used  in 
the  preparation  of  the  cells. 

One  thing  seemed  certain  at  the  outset  —  that  in  the  process 
of  moulding,  very  much  greater  pressure  must  be  employed 
than  that  commonly  used  in  the  potteries.  Air-blisters  or  cav- 
ities which  for  any  reason  might  otherwise  be  present,  would 
be  removed  by  this  treatment  and  the  density  of  the  cell  wall 
would  be  increased. 

The  improved  condition  of  the  air-dried  vessel  when  it  was 
placed  in  the  kiln  for  burning,  would  not,  however,  insure  the 
equally  perfect  quality  of  the  finished  product.  Indeed  it  was 
thought  probable  that  most  of  the  cavities  and  channels  might 
be  formed  during  the  process  of  burning,  for  if  the  chemically 
combined  water  in  the  clay  were  driven  off*  too  rapidly,  that 
which  was  liberated  at  any  point  beneath  the  surface  of  the  cell 

33 


34  THE    MEASUREMENT    OF    OSMOTIC    PRESSURE. 

wall  might  force  its  way  out  with  such  violence  as  to  form  the 
cavities  and  channels  which  were  so  often  met  with  in  the  ves- 
sels obtained  from  the  potters. 

If  the  true  cause  of  these  defects  was  the  rapid  expulsion  of 
the  chemically  combined  water  from  the  clay,  then  a  determin- 
ation of  the  temperature  at  which  this  reaction  took  place  most 
energetically  was  necessary,  and  a  furnace  capable  of  very  per- 
fect regulation  up  to  a  somewhat  higher  temperature  became 
essential. 

The  first  requisite  was  a  suitable  apparatus  for  forming  the 
cups  under  high  pressure.  The  following  brief  description  of 
the  mould  which  was  devised  and  used  by  Morse  and  Frazer 
will  serve  the  present  purpose.  The  details  of  its  construction 
will  be  published  in  another  place. 

THE  MOULD. 

The  strong  iron  vessel  14  cm.  in  diameter  and  13  cm.  deep, 
which  contains  the  mould  proper,  is  made  of  two  parts  sym- 
metrically situated  with  reference  to  an  imaginary  vertical  plane 
passing  through  the  center.  These  parts  can  be  securely  fas- 
tened together  by  means  of  bolts  on  the  sides.  In  this  iron 
vessel  the  plaster  of  Paris  mould,  with  the  cell-shaped  cavity 
in  the  center,  is  cast  in  two  parts  so  that  the  plane  of  their  sur- 
faces of  contact  coincides  with  the  vertical  plane  of  division  of 
the  containing  vessel. 

Around  the  upper  edge  of  the  vessel  extends  a  flat  rim  2.5 
cm.  in  width  and  to  this  an  iron  top  can  be  bolted,  through  the 
center  of  which  and  hence  directly  above  the  cavity  in  the 
plaster  of  Paris,  is  a  threaded  hole  8  cm.  in  depth  and  about 
3  cm.  in  diameter.  A  steel  plunger  23  cm.  in  length,  the 
lower  end  of  which  is  of  the  exact  size  and  shape  of  the  interior 
surface  of  the  cup,  is  threaded  at  the  upper  end  to  fit  the  hole 
and  can  be  raised  or  lowered  by  means  of  a  wrench. 

The  process  of  moulding  the  cup  consists  of  introducing  a 
sufficient  amount  of  moist  clay  into  the  plaster  mould,  of 


THE    ELECTRIC    FURNACE.  35 

roughly  shaping  the  clay  in  the  mould  with  the  fingers,  of 
bolting  the  iron  top  to  the  vessel  beneath  and  finally,  of  screw- 
ing down  the  plunger  to  a  proper  point  by  means  of  a  long- 
handled  wrench.  The  water  which  is  pressed  out  of  the  clay 
is  absorbed  by  the  plaster  of  Paris  and  the  cell  is  easily  taken 
from  the  mould,  after  the  withdrawal  of  the  plunger  and  the 
removal  of  the  top,  by  unscrewing  the  bolts  on  the  sides  of  the 
iron  vessel  and  carefully  separating  the  two  parts. 

DIMENSIONS  OF  THE  CUP. 

The  dimensions  of  the  cell  as  it  leaves  the  mould  are  as 
follows  :  length  93  mm. ;  internal  diameter  at  top  25  mm.  ; 
external  diameter  at  top,  including  rim,  37  mm.  ;  external 
diameter  at  top  just  below  rim  31  mm. ;  external  diameter  at 
bottom  24  mm. 

THE  ELECTRIC  FURNACE. 

The  temperature  at  which  the  three  varieties  of  clay  lost  fifty 
per  cent,  of  their  chemically  combined  water  was  determined  by 
means  of  an  electric  furnace  and  a  Le  Chatelier  pyrometer  to 
lie  between  the  limits  425°  and  450°.  If  then,  the  assump- 
tions made  above  were  in  accordance  with  the  facts,  it  would 
be  necessary  to  raise  the  temperature  very  slowly  between  these 
limits. 

Since  the  most  perfect  regulation  of  high  temperatures  is  best 
accomplished  in  the  electric  furnace,  and  since  the  instrument 
hitherto  employed  proved  to  be  somewhat  unsatisfactory,  a  suit- 
able furnace  had  to  be  devised. 

In  its  perfected  form  the  instrument  devised  in  this  laboratory 
by  Morse  and  Frazer  and  described  below,  has  proved  very 
efficient  for  use  up  to  a  temperature  of  about  1100°.  Above 
this  point  the  platinum  used  in  its  construction  volatilizes  to 
such  an  extent  that  repeated  heating  would  shorten  the  life  of 
the  wired  portion  to  an  unwarrantable  degree. 

The  form  and  size  of  the  furnace  may  be  varied  within 
very  wide  limits.  The  following  is  a  brief  description  of  the 


36  THE    MEASUREMENT   OF    OSMOTIC    PRESSURE. 

one  which  was  used  in  nearly  all  of  the  work  which  will  be 
detailed  in  the  following  pages. 

The  essential  parts  of  the  furnace  are  :  (1)  an  outer  cylinder 
of  sheet-iron  covered  both  within  and  without  with  asbestos 
paper ;  (2)  a  smaller  cylinder  of  fire-clay  ;  (3)  a  second  cylinder 
of  fire-clay  smaller  than  the  first ;  (4)  a  wired  portion  which 
forms  the  center  of  the  apparatus.  This  inner  wired  portion 
where  the  heat  is  generated  is  constructed  as  follows. 

Three  fire-clay  rings  are  held  in  horizontal  positions  one 
above  another  by  three  vertical  platinum  rods  11  cm.  in  length 
which  pass  through  holes  in  the  rings  and  are  threaded  at  both 
ends.  The  two  lower  rings  are  each  5  mm.  in  thickness  ;  the 
top  one  is  just  double  this  amount.  Each  threaded  portion  of 
the  rods  carries  two  platinum  nuts,  three  of  which  are  directly 
above  and  three  directly  below  the  top  and  bottom  ring  respec- 
tively. Another  important  role  which  these  rods  play  when 
the  furnace  is  in  use  will  be  pointed  out  later.  The  third  ring 
is  situated  midway  between  the  other  two  rings  and  is  fastened 
to  the  rods  with  platinum  wire.  The  middle  and  lowest  rings 
have  the  same  external  diameter  of  6.3  cm.,  but  the  internal 
diameter  of  the  lowest  one  is  smaller,  since  this  ring  forms  a 
support  for  objects  to  be  heated  in  the  furnace.  The  uppermost 
ring  has  the  same  internal  diameter  as  the  middle  one,  viz., 
4.5  cm.,  but  projects  beyond  the  other  two  by  an  amount  equal 
to  the  thickness  of  the  smaller  clay  cylinder  which  supports  it. 

Each  ring  is  perforated  with  a  double  series  of  concentric 
holes  5  mm.  apart,  and  through  these  two  pieces  of  number  26 
platinum  wire  (B.  &  S.  gauge),  each  about  3.6  meters  in  length, 
are  woven  up  and  down  and  across  the  bottom,  each  wire 
serving  to  wind  up  one  half  the  furnace. 

When  the  furnace  is  in  use  the  three  vertical  rods  previously 
mentioned  are  heated  very  nearly  to  the  temperature  of  the 
platinum  wires  through  which  the  current  is  passing,  and  con- 
sequently expand  to  nearly  the  same  extent.  The  distance 
between  the  top  and  bottom  rings  is  increased  proportionally 


THE    ELECTRIC    FURNACE.  37 

and  the  wires  are  thus  kept  straight  both  during  the  heating 
and  the  cooling  of  the  furnace.  This  arrangement  is  important, 
for  if  the  wires  were  not  straightened  as  they  are  expanded  by 
heat  there  would  be  danger  of  short-circuiting  the  current,  due 
to  contact  of  two  adjacent  wires.  These  rods  also  serve  to 
prevent  the  stretching  of  the  wires  which  might  take  place  at 
high  temperatures  if  the  weight  of  the  cell  which  rests  on  the 
lower  ring  were  not  supported  by  them. 

The  wired  portion  of  the  furnace  is  suspended  free  in  the 
smaller  cylinder  of  fire-clay,  previously  mentioned,  which  is 
12  cm.  in  height  and  7.8  cm.  outside  diameter.  The  lower 
end  of  the  cylinder  and  the  upper  ring  are  provided  with 
closely-fitting  discs  of  fire-clay. 

The  larger  clay  cylinder  which  surrounds  the  one  just  described 
and  is  separated  from  it  by  an  annular  air-space  of  1  cm.,  is  16 
cm.  in  height,  12  cm.  external  diameter,  and  about  1  cm.  in 
thickness.  This  is  fitted  with  a  top  and  bottom  like  the  inner 
cylinder.  Both  the  outer  and  inner  cylinders  are  supported, 
each  by  means  of  three  truncated  cones  of  fire-clay  1  cm.  in 
height. 

Surrounding  all'  is  a  cylinder  of  sheet-iron  covered  with 
asbestos  paper  and  provided  with  a  top  of  asbestos  board.  This 
cylinder  is  19.5  cm.  in  height  and  16  cm.  in  diameter,  and  rests 
upon  a  base  of  heavy  asbestos  board  beneath  which  is  a  soap- 
stone  slab. 

In  the  centers  of  the  three  cylinder  covers  are  holes  1.2  cm, 
in  diameter,  through  which  a  thermometer  or  the  clay  cylinder 
carrying  the  wires  of  the  thermo-couple  can  be  introduced. 

A  Le  Chatelier  pyrometer  connected  with  a  Keiser  and 
Schmidt  voltmeter  was  used  in  determining  the  temperature  of 
the  furnace  above  300°.  The  voltmeter  was  provided  with 
two  scales,  one  of  which  was  graduated  to  decimillivolts,  the 
other  for  direct  reading  of  the  temperature.  Each  division  of 
the  latter  scale  was  equivalent  to  20°,  so  that  the  temperature 
could  easily  be  estimated  to  within  two  or  three  degrees.  The 


38 


THE    MEASUREMENT    OF    OSMOTIC    PRESSURE. 


thermo-couple,  which  had  been  tested  at  the  Reichsanstalt,  was 
a  junction  of  platinum  and  platinum  containing  ten  per  cent, 
rhodium. 

CALIBRATION  OF  THE  ELECTRIC  FURNACE. 

The  depth  of  the  wired  portion  of  the  furnace,  that  is,  the 
distance  between  the  top  and  bottom  rings  was  just  sufficient 
for  the  introduction  of  one  of  the  clay  cups  which  rested  on  the 
lower  ring.  Since  there  was  no  room  for  the  thermo-couple 
when  the  cell  was  in  place,  a  calibration  of  the  empty  furnace 
became  necessary,  that  is,  the  maximum  temperature  obtain- 
able with  a  specified  current  had  to  be  determined  for  certain 
points  at  convenient  intervals  up  to  the  highest  temperature 
required  for  burning  the  cells.  The  strength  and  voltage  of 
the  current  having  been  determined  for  each  point,  the  corre- 
sponding resistance  of  the  furnace  and  the  electrical  energy  con- 
sumed in  maintaining  the  latter  at  this  temperature  could  be 
calculated,  and  from  these  data,  by  interpolation,  the  resistance 
and  disappearing  electrical  energy  for  all  intermediate  tem- 
peratures could  be  determined. 

The  results  of  the  calibration  are  presented  in  Table  VIII. 

TABLE  VIII. 


Amperes. 

Volts. 

Temp. 

Ohms. 

Joules. 

4.0 

18.0 

385° 

4.50 

72.00 

4.2 

19.8 

420 

4.71 

83.16 

4.4 

21.3 

446 

4.84 

93.72 

4.6 

23.3 

481 

5.07 

107.18 

5.4 

31.2 

617 

5.78 

168.48 

5.93 

36.9 

742 

6.22 

218.82 

6.53 

43.6 

845 

6.68 

284.71 

6.93 

48.4 

904 

6.98 

335.41 

The  method  of  calculating  the  resistance  for  temperatures 
not  given  in  the  table,  lying  between  385°  and  904°  may,  per- 
haps, be  best  illustrated  by  an  example. 

Suppose  it  is  required  to  find  the  resistance  of  the  furnace  for 
each  degree  lying  between  385°  and  420°.  The  resistance  for 
420°  was  4.71  ohms;  that  for  385°  was  4.50  ohms.  The 


CALIBRATION    OF   THE    ELECTRIC    FURNACE.  39 

increase  in  resistance  corresponding  to  an  increase  in  tempera- 
ture of  35®  is,  therefore,  4.71  —  4.50  =  0.21  ohm,  or  the  in- 
crease in  resistance  for  a  rise  of  1°  is  0.21  -j-  35  =  0.006  ohm. 
The  value  thus  obtained  is,  for  convenience,  called  the  "  re- 
sistance coefficient"  for  this  interval  of  35°.  The  increase  in 
the  number  of  joules  consumed  for  an  increase  of  1°  can  be 
calculated  in  a  similar  manner.  The  value  so  obtained  is 
termed  the  "energy  coefficient." 

The  resistance  for  temperatures  lying  between  385°  and 
420°  may,  therefore,  be  found  by  adding  to  4.50  ohms,  the  re- 
sistance at  385°,  0.006  ohm  for  each  rise  of  one  degree. 

Table  IX.  shows  the  resistance  and  energy  coefficients  for 
each  temperature  interval  given  in  the  first  column  of  Table 

VIII. 

TABLE  IX. 


Temperatures. 

Resistance  Coefficient. 

Energy  Coefficient. 

385-420° 
420-446 
446-481 
481-617 
617-742 
742-845 
845-904 

0.0060 
0.0050 
0.0066 
0.0052 
0.0035 
0.0045 
0.0051 

0.3189 

0.4062 
0.3845 
0.4507 
0.4027 
0.6397 
0.8593 

It  will  be  seen  from  the  data  given  in  Table  VIII.  that  it 
was  possible  to  prepare  a  table  containing  the  resistance  of,  and 
the  electrical  energy  consumed  in,  the  furnace,  for  each  degree 
between  385°  and  904°.  Conversely,  if  the  resistance  and 
disappearing  electrical  energy  were  known,  the  temperatures 
corresponding  to  each  could  be  determined  by  reference  to  the 
table. 

An  example  will,  perhaps,  make  the  method  of  procedure 
more  obvious.  In  burning  one  of  the  cells  the  current  used  at 
one  time  was  4.3  amperes  when  the  fall  in  potential  within  the 
furnace  was  20.2  volts.  The  resistance  calculated  from  these 
data  was  found  to  be  4.70  ohms,  and  the  electrical  energy  con- 
sumed to  be  86.86  joules.  By  reference  to  the  table  prepared 


40  THE    MEASUREMENT    OF    OSMOTIC    PRESSURE. 

according  to  the  method  described  above,  it  was  found  that  for 
a  resistance  of  4.70  ohms  the  temperature  was  418°  and  for 
86.86  joules  it  was  430°.  The  meaning  of  this  discrepancy 
between  the  results  obtained  by  the  two  methods  of  calculation 
is  explained  below. 

It  will  be  obvious  from  what  has  already  been  said  that 
when  the  furnace  had  once  been  accurately  calibrated  by  means 
of  the  thermo-couple,  its  temperature  at  any  subsequent  time 
could  be  calculated,  provided  only  the  current  flowing  in  the 
circuit  and  the  fall  in  potential  within  the  furnace  were  both 
known. 

Since  the  resistance  was  determined  by  the  value  of  the 
quotient  EjC,  in  which  E  represents  the  electromotive  force 
and  C  the  strength  of  the  current,  and  since  the  number  of 
joules  of  electrical  energy  disappearing  as  heat  is  determined 
by  the  value  of  the  product  E  x  (7,  it  would  at  first  sight 
seem  to  be  immaterial  whether  the  resistance  coefficient  or  the 
energy  coefficient  were  taken  as  the  basis  for  calculating  the 
temperature  of  the  furnace  at  any  time.  A  moment's  reflec- 
tion will,  however,  be  sufficient  to  show  that  these  two  methods 
would  give  the  same  result  only  when  the  electrical  energy, 
which  was  continually  being  transformed  into  heat  energy, 
.was  all  used  up  in  maintaining  the  temperature  of  the  furnace. 
If  this  were  not  the  case,  if,  for  instance,  some  of  the  heat 
energy  were  spent  in  vaporizing  water,  then  the  energy  avail- 
able for  maintaining  the  temperature  of  the  furnace  would  be 
diminished  by  just  this  amount  and  the  resistance  of  the  fur- 
nace would  consequently  be  less  than  would  otherwise  be  the 
case.  As  soon,  however,  as  all  the  water  were  vaporized,  the 
energy  available  for  maintaining  the  temperature  of  the  fur- 
nace would  be  increased  by  an  amount  equal  to  the  latent  heat 
of  vaporization  of  water ;  the  temperature  of  the  furnace  would 
rise  and  the  resistance  would  increase. 

This  was  exactly  what  proved  to  be  the  case  when  the  air- 
dried  cells  were  burned.  With  each  increase  of  current,  the 


THE    GAS    FURNACE.  41 

temperature  as  calculated  from  the  resistance  was  at  first  lower 
than  that  calculated  from  the  electrical  energy  which  was  used  up 
in  the  furnace,  but  gradually  increased  until  the  two  were  nearly 
or  quite  equal.  When  the  current  was  raised  again  the  same 
phenomenon  was  observed  and  so  on  to  the  end.  It  thus  be- 
came possible  to  determine  the  end  of  the  reaction  which  re- 
sulted in  the  expulsion  of  the  chemically  combined  water  in  the 
clay,  and  to  regulate  the  current  accordingly. 

In  this  connection,  however,  it  must  not  be  forgotten  that  a 
certain  time  is  required  to  raise  the  temperature  of  the  furnace 
to  the  maximum  obtainable  with  any  specified  current,  and  that, 
consequently,  even  with  an  empty  furnace,  the  temperature  cal- 
culated from  the  resistance  would  be  lower  than  that  calculated 
from  the  disappearing  electrical  energy,  until  equilibrium  were 
established.  By  measuring  the  time  required  to  bring  about 
this  state  of  equilibrium  a  more  correct  idea  could  be  formed  of 
the  energy  changes  which  accompany  a  reaction  within  the  fur- 
nace. 

An  exothermic  reaction  should  have  an  effect  just  the  oppo- 
site of  the  endothermic  one  described  above ;  that  is,  the  heat 
which  is  evolved  when  the  reaction  takes  place  must  raise  the 
temperature  of  the  furnace  and  hence  produce  an  increase  in 
the  resistance  of  the  wires.  The  temperature  calculated  from 
the  resistance  would,  in  this  case,  be  greater  than  that  calculated 
from  the  amount  of  electrical  energy  consumed. 

The  principle  involved  in  these  phenomena  seems  capable  of 
extensive  application  and  experiments  already  carried  out  or 
now  in  progress  in  this  laboratory  justify  the  hope  that  it  will 
contribute  much  to  our  knowledge  of  reactions  which  take 
place  at  high  temperatures. 

THE  GAS  FURNACE. 

It  has  already  been  stated  that  the  electric  furnace  could  not 
be  used  advantageously  at  temperatures  above  1100°  or  there- 
about, owing  to  the  volatility  of  the  platinum.  It  was,  how- 


42 


THE    MEASUREMENT    OF    OSMOTIC    PRESSURE. 


ever,  necessary  to  burn  the  cells  at  about  1300°.  For  obtain- 
ing these  higher  temperatures  a  modified  form  of  the  Seger  gas 
furnace  was  used  and  its  temperature  ascertained  by  means  of 
Seger  cones.  The  quantity  of  gas  consumed  in  the  production 
of  a  temperature  just  sufficient  to  soften  one  of  the  cones  was 
measured  with  an  ordinary  twenty-light  gas  meter. 

Table  X.  contains  the  results  of  some  observations  made  on 
the  calibration  of  this  furnace. 

TABLE  X. 


Cubic  Feet  Gas  Consumed 
per  Hour. 


Temperature  of  Furnace. 


41 
51 
60 
71 


(about)  800° 
950 
1090 
1290 


Owing  to  the  fact  that  the  gas  pressure  was  never  perfectly 
constant,  the  figures  given  in  the  first  column  represent  only 
approximately  the  true  values. 

OBSERVATIONS  ON  THE  BURNING  OF  CELLS. 

With  the  exception  of  the  cell  VI.  mentioned  below,  all  of 
the  cells  described  in  the  following  pages  were  moulded  under 
high  pressure  in  the  manner  described  on  pages  34  and  35. 

The  three  varieties  of  clay  obtained  from  D.  F.  Haynes  & 
Son  for  the  preparation  of  the  porous  cups,  are  known  as 

TABLE  XI. 


Florida  Clay. 

Peach  Clay. 

Eng.  Ball  Clay. 

H20 
Si02 
A1A 

13.35 

46.07 

38.48 

12.28 
48.09 
35.78 

11.91 
49.38 
35.19 

Fe 

1.84 



CaO 

0.24 



MgO 

0.26 

Trace 

... 

K20 

1.88 

2.36 

2.54 

Na20 







C 

0  4 

......* 

100.28 

100,75 

99.02 

OBSERVATIONS    ON    THE    BURNING    OF   CELLS. 


43 


Peach,  Delaware ;  Edgar,  Florida ;  and  English  Ball  clay. 
These  clays,  after  washing  and  bolting,  were  analyzed  by  Mr. 
L.  S.  Taylor,  to  whom  the  writer  is  indebted  for  the  data  pre- 
sented in  Table  XI.  The  figures  express  percentages. 

Cup  I.  —  The  composition  of  this  cell  was  Delaware  clay 
without  the  admixture  of  silica,  feldspar  or  other  clays.  It 
was  dried  in  the  air  for  an  unknown  time,  but  certainly  for 
thirty-six  hours,  before  being  heated  in  the  electric  furnace. 

The  cell  was  placed  in  the  furnace  at  9  a.  m.  on  November 
23.  The  initial  current,  which  was  not  recorded,  was  raised 
very  gradually,  until  at  4:30  p.  m.,  it  was  4.4  amperes. 

Table  XII.  contains  a  few  of  the  data  obtained  in  burning 
this  cup. 

TABLE  XII. 


Time. 

Amperes. 

Volts. 

Ohms. 

Joules. 

Tempera- 
ture 
Found. 

Temp, 
from 
Elec. 
Energy. 

November  23. 

4  :  30  p.  m. 

4.42 

21.1 

4.77 

93.26 

434° 

443° 

7:30    " 

4.40 

21.4 

4.86 

94.16 

449 

450 

10:30     " 

4.50 

22.2 

4.93 

99.90 

461 

461 

November  24. 

6  :  00  a.  m. 

4.51 

22.3 

4.94 

100.57 

463 

463 

12  :  50  p.  m. 

4.65 

23.8 

5.12 

110.67 

487 

489 

5:30     " 

5.00 

26.8 

5.36 

134.00           537 

540 

8:30     " 

5.10 

27.6 

5.41 

140.76 

548 

558 

November  25. 

6  :  30  a.  m. 

5.10 

27.8 

5.45 

141.78 

556 

559 

12  :  30  p.  m. 

5.2 

29.1 

5.60 

151.32 

582 

579 

6:30     " 

5.6 

33.2 

5.93 

185.92 

660 

660 

9:00     " 

6.0 

37.3 

6.21 

223.80 

743 

750 

9:40     " 

6.0 

37.5 

6.26 

225.00 

750 

752 

12  :00  night. 

6.4 

41.6 

6.50 

266.24 

804 

816 

November  26. 

12  :30  a.  m. 

6.4          41.7 

6.52 

266.88 

808 

817 

1:00     " 

6.4      !    41.8 

6.53 

267.52 

;an 

818 

4:05     " 

6.9 

47  .4 

6.87 

327.06 

882 

894 

The  last  figures  in  column  VII.  indicate  the  highest  temperature  at  which 
the  cell  was  burned  in  the  electric  furnace. 

The  current  was  diminished  very  slowly  in  order  to  lessen 
the  danger  of  cracking  the  cell,  which  was  removed  when  quite 
cool,  and  a  few  days  later  was  placed  in  the  gas  furnace  for 


44  THE    MEASUREMENT    OF    OSMOTIC    PRESSURE. 

the  final  burning.  Here  also  care  was  taken  to  raise  the  tem- 
perature slowly  to  the  maximum  which  was  maintained  for 
about  sixteen  hours  and  then  the  supply  of  gas  was  gradually 
lessened  until,  in  thirty  hours  from  the  beginning  of  the  burn- 
ing, it  was  shut  off  completely. 

Highest  temperature  of  furnace  not  known,  but  certainly 
below  1290°,  as  determined  by  the  Seger  cones.  Length  of 
cell  after  burning  3.58  inches.  It  was  evident  both  from  the 
moderate  shrinkage  of  the  cup  and  its  great  porosity  when 
tested  with  the  tongue  that  it  had  not  been  burned  at  a  suffi- 
ciently high  temperature.  It  was  reburned  in  the  gas  furnace 
for  thirty-three  and  one-half  hours,  the  maximum  temperature 
of  1270°  being  maintained  for  about  ten  hours. 

Length  of  cell  upon  removal  from  furnace  3.45  inches. 
Shrinkage  during  second  burning  in  gas  furnace  3.6  per  cent. 

When  filled  with  water  the  whole  exterior  surface  of  the  cell 
became  moist  at  the  same  time,  indicating  that  the  walls  were 
quite  uniformly  porous.  When  the  same  test  was  applied  to 
the  bottle-shaped  cells,  certain  areas  of  the  walls  were  frequently 
found  to  be  either  impervious  to  water  or  at  least  very  much 
less  porous  than  other  portions. 

An  attempt  was  made  to  deposit  a  membrane  of  copper  fer- 
rocyanide  in  this  cell,  but  when  the  resistance  had  reached 
4,800  ohms,  it  was  discovered  that  the  cell  was  cracked. 
Whether  this  crack  was  produced  during  the  burning  of  the 
cell  or  by  subsequent  treatment,  is  not  surely  known,  but  the 
latter  is  believed  to  be  the  case.  To  those  whose  greatest  diffi- 
culty thus  far  has  been  to  prepare  a  suitable  cell  free  from 
cracks,  this  apparently  insignificant  fact  seems  worthy  of 
mention, 

The  vessel  was  broken  and  the  fractured  surfaces  were  ex- 
amined. The  walls  seemed  to  be  very  free  from  cavities  and 
channels,  but  were  also  deficient  in  strength. 

Cup  II. — The  composition  of  this  cup  was  the  same  as  that 
of  I,  viz.,  Delaware  clay  without  any  admixture  of  other  ma- 


OBSERVATIONS    ON    THE    BURNING    OF    CELLS.  45 

terials,  and  like  it,  was  dried  in  the  air  at  ordinary  tempera- 
ture before  being  placed  in  the  electric  furnace. 

The  initial  current  of  1.7  amperes  was  gradually  increased 
until  in  eight  days  three  and  one-half  hours  the  maximum 
temperature  was  reached.  The  observations  made  at  this  time 
were  as  follows  :  current,  6.5  amperes;  electromotive  force,  43 
volts ;  resistance,  6.61  ohms  ;  temperature  calculated  from  re- 
sistance, 830°  ;  electrical  energy  consumed  in  the  furnace, 
279.5  joules  ;  temperature  calculated  from  disappearing  elec- 
trical energy,  836°. 

The  cell  was  next  burned  in  the  gas  furnace  at  a  maximum 
temperature  of  1310°,  the  customary  precaution  being  taken 
to  insure  the  gradual  raising  and  lowering  of  the  temperature. 

Length  of  cell  when  taken  from  the  electric  furnace  3.66 
inches.  Length  of  cell  when  taken  from  gas  furnace  3.34 
inches.  Shrinkage  of  cell  in  gas  furnace  8.7  per  cent. 

Although  some  slight  cracks  were  visible  in  the  walls  of  this 
cell,  it  was  thought  that  some  idea  of  its  porosity  and  of  its 
suitability  as  a  support  for  a  semipermeable  membrane  might 
be  obtained  by  an  attempt  to  deposit  in  it  a  membrane  of  copper 
ferrocyanide.  The  methods  employed  were  essentially  those 
which  were  described  in  Part  I.  of  this  dissertation.  Instead, 
however,  of  using  a  small  voltage  at  the  beginning,  a  current 
at  109  volts  was  employed  throughout  the  process  of  membrane 
formation.  The  maximum  resistance  of  99,400  ohms  was  de- 
veloped in  one  hour.  At  the  end  of  three  hours  the  resistance 
had  decreased  to  84,000  ohms. 

The  cell  was  filled  with  a  half  normal  solution  of  cane  sugar 
and  set  up  essentially  in  the  manner  described  by  Morse  and 
Frazer.1  Practically  no  pressure  was  developed  within  the 
cell. 

An  attempt  was  made  to  reenforce  the  membrane  by  means 
of  a  current  of  109  volts  which  was  passed  for  two  hours.  The 
final  resistance  was  only  13,600  ohms  and  as  it  had  been  de- 

1  Am.  Chem.  Jour.,  28,  3. 


46          '     THE    MEASUREMENT    OF    OSMOTIC    PRESSURE. 

creasing  from  the  very  first,  the  circuit  was  broken  and  the 
cell  was  again  set  up  with  a  half  normal -sugar  solution.  In 
nine  hours  a  pressure  of  112  mm.  of  mercury  had  been 
developed. 

The  cell  was  broken  and  the  fractured  edges  of  the  wall 
were  examined.  These  showed  a  distinct  line  of  cleavage  run- 
ning parallel  with  the  longitudinal  axis  of  the  cup  and  about 
midway  between  the  two  surfaces.  Except  where  the  two 
layers  met,  the  wall  seemed  dense  and  free  from  air-blisters. 

The  cause  of  the  above-mentioned  defect  in  the  moulding  of 
the  cup  is  not  certainly  known,  but  it  is  believed  to  be  due  to 
the  use  of  an  excess  of  clay  at  the  top  of  the  cell.  If  the  in- 
terior diameter  of  the  cup  were  left  too  small  by  the  preliminary 
shaping  with  the  fingers,  the  descending  plunger  might  carry 
some  of  this  excess  of  clay  before  it  until  the  bottom  was 
reached.  By  further  advancement  of  the  plunger  this  super- 
fluous clay  would  be  forced  upward  under  great  pressure  and 
spread  over  the  clay  which  formed  the  original  wall  and  from 
which  in  the  meantime,  the  water  had  been  partially  absorbed 
by  the  plaster  of  Paris.  The  final  effect  would,  therefore,  be 
the  formation  of  a  wall  consisting  of  two  layers  which  under 
the  circumstances  could  hardly  be  expected  to  form  a  homo- 
geneous whole. 

With  the  hope  of  preventing  the  formation  of  this  double 
layer,  the  mould  has  been  somewhat  modified,  but  as  no  cups 
have  been  formed  in  it  since  the  changes  were  made  the  bene- 
fits to  be  derived  are  as  yet  only  a  matter  of  conjecture. 

Cup  III.  —  This  cup,  like  cups  I.  and  II.,  was  of  Delaware 
clay  without  admixture  of  quartz,  feldspar  or  other  clays,  and 
its  treatment  preliminary  to  heating  was  similar  to  that  recorded 
for  the  two  cups  just  mentioned. 

The  dehydration  was  accomplished  in  an  electric  furnace 
which  differed  from  the  one  described  on  pages  35-36  only  in 
minor  details,  and  which  had  been  calibrated  by  Dr.  Frazer. 

In  the  burning  of  this  cup  thp  current  was  gradually  raised 


OBSERVATIONS    OX    THE    BURNING    OF    CELLS. 


47 


during  the  course  of  four  days  three  and  one-half  hours,  from 
2.4  to  6.94  amperes.  The  last  reading  was  as  follows :  cur- 
rent, 6.94  amperes  ;  electromotive  force,  46.0  volts  ;  resistance, 
6.63  ohms ;  temperature  calculated  from  resistance,  833°; 
electrical  energy  consumed  in  the  furnace,  319.24  joules  ;  tem- 
perature calculated  from  disappearing  electrical  energy,  885°. 

This  cell  was  burned  with  cell  II.  in  the  gas  furnace  at  a 
maximum  temperature  of  1310°.  Length  of  cell  upon  removal 
from  the  electric  furnace,  3.62  inches.  Length  of  cell  upon 
removal  from  gas  furnace,  3.34  inches.  Shrinkage  of  cell  in 
gas  furnace  7.7  per  cent. 

This  cell  was  found  to  be  cracked  in  several  places  and  was 
unfit  for  further  tests. 

Cup  IV.  —  This  cup  was  of  English  Ball  clay  without  admix- 
ture of  other  materials.  It  was  dried  in  the  usual  manner 
before  being  introduced  into  the  electric  furnace. 

The  initial  current  was  1.2  amperes.  Three  days  two  and 
one-half  hours  were  consumed  in  reaching  the  highest  tempera- 
ture of  the  furnace,  viz.,  851°. 

Some  of  the  observations  which  were  made  on  the  dehydra- 

TABLE  XIII. 


Time. 

Amperes. 

Volts. 

Ohms. 

Joules. 

Temper- 
ature 
Found. 

Temp,  from 
Electrical 
Energy 

Consumed. 

3  :  40  p.  m. 

4.3 

19.5 

4.53 

83.85 

390° 

422° 

3:50 

4.3 

19.7 

4.58 

84.71 

398 

424 

4:00 

4.3 

19.8 

4.60 

85.14 

402 

425 

4:30 

4.3 

20.0 

4.65 

86.00 

410 

427 

5  :05 

4.3 

20.2 

4.70 

86.86 

418 

430 

10  :  10  a   m. 

4.3 

20.4 

4.74 

87.72 

427 

431 

10:30 

4.4 

21.2 

4.82 

93.28 

442 

445 

11:00 

4.5 

22.0 

4.89 

99.00 

453 

460 

11  :20 

4.5 

22.15 

4.92 

99.67 

459 

461 

tion  of  this  cell  between  400°  and  460°  are  presented  in  Table 
XIII.  It  will  be  noticed  that  for  a  current  of  4.3  amperes, 
the  maximum  difference  between  the  temperature  calculated 
from  the  resistance  of  the  furnace  and  the  electrical  energy 


48  THE    MEASUREMENT    OF    OSMOTIC    PRESSURE. 

consumed  in  it,  is  gradually  diminished  from  32°  to  4°.  It  is 
to  be  borne  in  mind,  however,  that  not  all  of  the  energy  repre- 
sented by  these  differences,  particularly  in  the  first  case,  is  con- 
sumed in  expelling  the  water  of  the  clay  in  the  condition  of 
vapor.  A  portion  of  it  is  spent  in  raising  the  temperature  of 
the  furnace. 

During  the  first  part  of  the  cooling  of  the  furnace  the  tem- 
perature was  reduced  0.05  ampere  at  a  time,  at  the  rate  of 
0.4  ampere  per  hour.  At  the  end  of  twenty-five  hours  the  cir- 
cuit was  broken.  Length  of  cell  before  heating,  3.59  inches. 
Length  of  cell  after  heating,  3.56  inches.  Shrinkage  of  cell  in 
electric  furnace,  0.8  per  cent. 

Upon  careful  examination  the  cup  was  found  to  be  cracked 
and  hence  was  not  burned  in  the  gas  furnace.  It  has  been 
found  that  even  extremely  minute  cracks  are  a  fatal  defect  in 
porous  vessels  which  are  employed  in  the  investigation  of 
osmotic  pressure.  For  this  reason  all  the  cups  were  examined 
internally  with  great  care  by  the  aid  of  a  small  electric  lamp. 

Cup  V.  —  Each  of  the  cups  previously  described  had  con- 
sisted of  only  a  single  variety  of  clay.  It  was  now  determined 
to  try  the  effect  of  mixing  three  different  clays.  Accordingly 
equal  parts  by  weight  of  Peach,  Delaware  ;  Edgar,  Florida ; 
and  English  Ball  clays  were  very  thoroughly  mixed  and  a  por- 
tion of  the  material  thus  prepared  was  used  for  cup  V.,  which 
was  dried  at  a  temperature  of  40°  in  a  large  air-bath  provided 
with  a  stirrer  which  kept  the  air  in  constant  circulation. 

Before  placing  the  cup  in  the  electric  furnace  it  was  very 
carefully  examined  on  the  interior  as  well  as  on  the  exterior, 
but  no  cracks  were  to  be  found. 

The  initial  current  was  1 .4  amperes.  During  two  and  one- 
sixth  days  the  current  was  slowly  increased  to  6.6  amperes  and 
was  maintained  at  this  point  for  the  succeeding  eighteen  hours. 
From  the  last  reading  recorded  at  the  time  the  following  data 
are  taken  :  current,  6.6  amperes  ;  electromotive  force,  43.9 
volts ;  resistance,  6.65  ohms  ;  temperature  calculated  from  re- 


OBSERVATIONS    ON    THE    BURNING    OF   CELLS.  49 

sistance,  838°  ;  electrical  energy  consumed  in  furnace,  289.74 
joules  ;  temperature  calculated  from  energy  consumed,  851°. 

The  current  was  decreased  0.05  ampere  at  a  time,  at  a  rate 
not  exceeding  0.2  ampere  per  hour  until  it  stood  at  5.5  amperes. 
The  total  time  occupied  in  reducing  the  current  to  zero  was 
twenty-seven  hours.  Length  of  air-dried  cell,  3.59  inches. 
Length  of  cell  upon  removal  from  electric  furnace,  3.55  inches. 
Shrinkage  of  cell  in  electric  furnace.  1.1  per  cent. 

Externally  the  cell  appeared  to  be  quite  perfect,  but  an  ex- 
amination of  the  interior  surface  revealed  the  presence  of  a 
crack  more  than  2  cm.  in  length.  When  burned  in  the  kiln  of 
D.  F.  Haynes  &  Son  this  cell  was  reduced  in  length  to  3.14 
inches  and  the  crack,  as  was  anticipated,  increased  in  size. 

Total  shrinkage  in  cell,  12.5  percent.  The  cell  wall  showed 
the  same  unsatisfactory  structure  which  was  mentioned  in  the 
description  of  cup  II.,  viz.,  a  distinct  line  of  cleavage  run- 
ning parallel  with  the  longitudinal  axis  and  about  half  way 
between  the  two  surfaces. 

Cap  VI.  —  The  composition  of  this  cup  was  the  same  as 
that  of  cup  V.,  viz.,  a  mixture  of  equal  parts  of  Delaware, 
Florida  and  English  Ball  clays.  It  was,  however,  not  moulded 
under  high  pressure,  but  was  shaped  to  the  mould  with  the 
fingers.  Like  the  cup  last  described,  it  was  dried  in  the  air- 
bath  before  being  heated  in  the  electric  furnace. 

The  highest  current  used  in  dehydrating  the  clay  of  which 
this  cup  was  composed  was  6.75  amperes,  but  the  voltage  was 
not  read  for  any  current  above  6.6  amperes.  The  maximum 
temperature,  therefore,  to  which  the  furnace  was  raised  is  un- 
known. For  the  current  of  6.6  amperes  the  electromotive 
force  was  43.4  volts.  The  following  data  are  based  upon  these 
readings  :  resistance,  6.58  ohms  ;  temperature  calculated  from 
resistance,  822°  ;  electrical  energy  consumed  in  furnace,  286.44 
joules ;  temperature  calculated  from  disappearing  electrical 
energy,  847°. 

The  current  was  raised  rather  more  rapidly  than  usual  during 


50  THE    MEASUREMENT    OF    OSMOTIC    PRESSURE. 

the  last  part  of  the  heating,  and  to  this  fact  is  undoubtedly  to 
be  attributed  the  large  difference  between  the  temperatures 
calculated  by  the  two  methods. 

When  the  furnace  was  left  for  the  night  at  10  p.  m.,the  cur- 
rent was  6.7  amperes.  At  ten  o'clock  the  next  morning,  when 
the  current  began  to  be  reduced,  it  had  fallen  to  6.4  amperes. 
Twenty-seven  hours  later  the  circuit  was  broken.  Although 
this  cell  contained  a  small  crack  it  was  further  burned  together 
with  cup  V.  in  the  kiln  of  D.  F.  Haynes  &  Son.  In  this 
case  also,  the  crack  was  considerably  increased  in  size  by  this 
further  heating. 

Length  of  air-dried  cell,  3.62  inches ;  on  removal  from  elec- 
tric furnace,  3.57  inches;  on  removal  from  pottery  kiln,  3.19 
inches.  Shrinkage  of  cell  in  electric  furnace,  1.4  per  cent. 
Total  shrinkage,  11.9  per  cent. 

The  appearance  of  the  fractured  edges  of  this  cup,  when 
broken,  was  more  unsatisfactory  than  that  of  the  cups  which 
were  moulded  under  high  pressure.  Minute  cavities  were  abun- 
dant, thus  showing  that  pressure  cannot  safely  be  dispensed 
with  in  the  moulding  of  the  cups. 

Cup  VII.  —  A  mixture  of  unknown  composition  obtained 
from  D.  F.  Haynes  &  Son,  and  called  by  them  "  semi-porcelain 
mixture"  was  used  in  the  preparation  of  this  cup.  It  was 
dried  in  the  air  at  ordinary  temperatures  and  then  introduced 
into  the  electric  furnace. 

The  initial  current  used  was  less  than  two  amperes.  Three 
and  a  quarter  days  were  required  to  reach  the  maximum  cur- 
rent of  9.1  amperes.  Owing  to  unsteadiness  of  current,  the 
ammeter  and  voltmeter  could  not  be  read  with  the  usual  accur- 
acy at  the  maximum  temperature  of  the  furnace.  The  errors 
which  were  as  a  consequence  introduced  into  the  calculation 
of  the  resistance,  were  greatly  increased  by  the  necessity  of 
extrapolation,  owing  to  the  fact  that  since  making  some  repairs 
in  the  furnace,  due  to  the  fusion  of  one  of  the  platinum  wires, 
it  had  not  been  calibrated  for  temperatures  above  904°. 


OBSERVATIONS    ON    THE    BURNING    OF    CELLS.  51 

The  following  data  are  based  upon  the  last  reliable  readings 
of  ammeter  and  voltmeter,  viz.,  current,  9.1  amperes;  electro- 
motive force,  77.1  volts.  Resistance,  8.47  ohms;  temperature 
calculated  from  resistance,  1200°  ;  electrical  energy  consumed 
in  furnace,  770.77  joules.  In  all  probability,  the  resistance 
did  not  rise  more  than  a  few  hundredths  of  an  ohm  above  8.5 
ohms. 

It  should  further  be  stated  that  in  addition  to  the  unfortunate 
circumstances  already  mentioned,  an  accident  occurred  when  the 
temperature  of  the  furnace  was  between  800°  and  900°  which 
must  have  occasioned  a  rather  rapid  lowering  of  the  tempera- 
ture for  an  unknown  time  and  to  an  unknown  degree.  It  was, 
therefore,  not  surprising  to  find,  upon  removal  of  the  cup  from 
the  furnace,  that  it  contained  numerous  cracks.  It  was  also 
completely  converted  into  porcelain.  The  outside  of  the  cup 
was  covered  with  glistening  particles  somewhat  resembling  frost 
and  the  inside  of  the  smaller  clay  cylinder  surrounding  the 
wired  portion  of  the  furnace  had  the  same  appearance.  There 
can  be  little  doubt  that  the  formation  of  these  particles  was  due 
to  the  volatilization  of  the  platinum  or  some  impurity  contained 
in  it.  Length  of  air-dried  cell,  3.66  inches.  Length  of  cell, 
after  the  burning  in  electric  furnace,  3.35  inches.  Shrinkage 
of  cell  in  electric  furnace,  8.4  per  cent. 

The  "semi-porcelain  mixture"  seems  to  be  quite  unfit  for 
use  in  the  construction  of  cups  suitable  for  the  measurement  of 
osmotic  pressure,  owing  to  the  relatively  low  temperature  at 
which  it  fuses. 

Cap  VIII.  —  The  composition  of  this  cup  was  the  same  as 
that  of  cups  V.  and  VI.,  viz.,  equal  parts  of  Delaware,  Florida, 
and  English  Ball  clays.  It  was  dried  in  the  air  at  a  tempera- 
ture not  above  40°  before  being  introduced  into  the  electric 
furnace. 

Since  the  burning  of  this  cup  was  unsatisfactory,  owing  to 
an  accident,  details  will  not  be  given.  The  highest  tempera- 
ture of  the  furnace  was  about  865°.  The  cell  was  badly 


52  THE    MEASUREMENT   OF    OSMOTIC    PRESSURE. 

cracked  but  the  texture  of  the  wall,  as  far  as  freedom  from 
blisters,  channels,  etc.,  was  concerned,  was  excellent. 

Cup  IX.  —  This  cup  was  composed  of  the  semi-porcelain 
mixture  used  in  the  formation  of  cup  VII.  It  was  not  burned 
in  the  electric  furnace  but  was  buried  in  sand  and  heated  prob- 
ably to  about  1100°  in  the  gas  furnace.  No  Seger  cones  were 
used  and  as  one  or  two  of  the  burners  were  defective,  it  is  pos- 
sible that  the  temperature  was  lower  than  that  mentioned  above. 
The  maximum  temperature  of  the  furnace  was  maintained  for 
about  seventeen  hours.  Six  and  one-half  hours  after  the  proc- 
ess of  cooling  was  begun  the  gas  was  shut  oif. 

Upon  removal  from  the  furnace  the  cup  was  found  to  con- 
tain a  crack  near  the  bottom.  It  was  porous  and  fairly  strong. 
Length  3.52  inches. 

When  an  attempt  was  made  to  deposit  a  membrane  of  copper 
ferrocyanide  in  the  cup,  phenomena  similar  to  those  which  had 
been  previously  noticed  in  the  case  of  very  porous  vessels 
immediately  appeared.  The  current  rose  rapidly  and  the 
liquid  in  the  cell  soon  became  turbid  with  a  precipitate  of  the 
ferrocyanide  of  copper.  To  each  liter  of  the  tenth  normal 
potassium  salt  used  in  this  experiment,  10  cc.  of  acetic  acid 
had  been  added.  The  second  attempt  to  deposit  the  same 
membrane,  using  a  neutral  solution  of  the  potassium  ferrocyan- 
ide, resulted  also  in  failure.  As  soon  as  the  electromotive 
force  was  raised  to  50  volts,  the  current  began  to  rise  rapidly 
and  even  when  the  voltage  was  kept  below  30,  the  same  effect 
was  produced  to  a  smaller  extent.  For  instance,  in  the  course 
of  an  hour,  with  an  electromotive  force  varying  from  28  to  29 
volts,  the  resistance  decreased  from  1,812  to  1,439  ohms. 

The  cell  was  set  up  with  a  half  normal  solution  of  sugar,  but 
the  membrane  exhibited  no  osmotic  pressure. 

Cup  X.  —  The  mixture  used  for  this  cup  consisted  of  clay, 
feldspar  and  flint  in  the  following  proportions  :  55.35  per  cent, 
of  equal  parts  by  weight  of  Delaware,  Florida,  and  English 
Ball  clays;  31.25  per  cent,  flint;  13.39  per  cent,  feldspar. 


OBSERVATIONS    ON    THE    BURNING    OF    CELLS.  53 

The  cup  was  moulded  under  pressure  and  dried  for  ten  days 
at  the  temperature  of  the  room,  in  a  cylinder  made  of  plaster 
of  Paris.  Previous  experience  had  shown  that  the  evaporation 
of  the  water  used  in  mixing  the  clay  was  so  slow  and  uniform 
under  these  conditions  that  the  cracking  which  was  very  apt  to 
take  place  during  the  desiccation  in  air  was  almost  wholly 
prevented. 

The  cylinder  containing  the  cup  was  then  placed  for  a  time 
in  the  air-bath,  which  was  kept  at  a  temperature  of  50°.  The 
cup  was  buried  in  sand  and  burned  in  the  gas  furnace  to  a 
temperature  of  1310°.  The  maximum  temperature  of  the  fur- 
nace was  maintained  for  about  seven  and  one-half  hours. 
Total  time  of  heating,  forty-eight  hours. 

Upon  opening  the  furnace  the  sand  was  found  to  be  baked 
so  hard  that  it  was  necessary  to  dig  it  out  with  a  knife.  The 
cup  was  cracked  in  several  places  and  had  passed  over  into 
porcelain.  The  shrinkage  was  not  determined,  owing  to  the 
breaking  of  the  cup  in  an  attempt  to  remove  the  sand  which 
filled  it. 

While  the  foregoing  experiments  do  not,  taken  by  them- 
selves, appear  to  contribute  very  largely  to  the  solution  of  the 
very  difficult  problem  which  is  under  investigation  in  this 
laboratory,  they  are  to  be  considered  as  a  necessary  part  of  the 
work  which  must  be  accomplished  before  the  obstacles  which 
present  themselves  in  this  field  are  successfully  overcome. 


BIOGRAPHY. 

The  writer  was  born  in  Kiantone,  New  York,  on  October 
21,  1873.  His  early  education  was  obtained  in  the  schools  of 
Jamestown,  New  York.  In  1896  he  was  graduated  from 
Amherst  College  with  the  degree  of  Bachelor  of  Arts.  Since 
October,  1899,  with  the  exception  of  a  year  spent  in  teaching 
chemistry  at  Cornell  University,  he  has  pursued  graduate 
studies  in  chemistry  at  the  Johns  Hopkins  University.  In 
1903-1904  he  held  a  fellowship  in  chemistry.  His  subordi- 
nate subjects  have  been  physical  chemistry  and  geology. 


54 


